They ruled from Pataliputra. Taxila was the capital of the province of Gandhara under Mauryan rule. If you are saying otherwise, post references.
Which ones? Name a few well-known western historians?
I wasnt going to reply because i know you are not going to believe it then i thought lets give a final try.
There is school of scholars like B.M. Barua, Dr J.W. McCrindle, Dr D.B. Spooner, Dr H.C. Seth, Dr Hari Ram Gupta, Dr Ranajit Pal and others who connect Chandragupta (Sandrokottos) to the north-western frontiers(Pakistan). B.M. Barua calls him a man of Uttarapatha or Gandhara if not exactly of Taksashila
Source: 'To me Candragupta was a man of the Uttarapatha or Gandhara if not exactly of Taksashila' (Indian Culture, vol. X, p. 34, B. M. Barua).
Based on Plutarch's evidence, Dr J.W. McCrindle and Dr H. R. Gupta write that Chandragupta Maurya was a Punjabi and belonged to the Ashvaka (Assakenoi) territory.
Source: Invasion of India by Alexander the great, p. 405. Plutarch attests that Androcottos had seen Alexander when he (Androcottos) was a lad and afterwards he used to declare that Alexander might easily have conquered the whole country (India); Was Chandragupta Maurya a Punjabi? Article in Punjab History Conference, Second Session, Oct 28-30, 1966, Punjabi University Patiala, p 32-35
Appian of Alexandria (95CE-165CE), author of a Roman History attests that 'Antrokottos (Chandragupta), the king of the Indians, dwelt on river Indus'.
Source: Appian (XI, 55). Some historians state that he belonged to Kunar and Swat valleys. See: The Kambojas Through the Ages, 2005, pp 150-51, Kirpal Singh. This reference also seems to indicate that Chandragupta belonged to north-west rather than East India.
These scholars relate Sandrocottos (or Androcottos) with Sisicottos of the Classical writings. Sisicottos was the ruler of Paropamise (Hindu Kush) who had helped Bessus of Bactria against Alexander but later co-operated with the latter throughout the Sogdian campaigns.
Source Arrian. iv, 30. 4
During Alexander's campaign of Kabol and Swat valleys, prince Sisicottos had rendered great service to Alexander in reducing several principalities of the Ashvakas. During war of rock-fort of Aornos, where Alexander faced stiff resistance from the tribals, Sisicottos was put in command of this fort of great strategical importance. Arrian calls Sisicottos the governor of Assakenois. It is however not quite clear if this Sisicottos was same as Sandrocottos or if they were brothers or else they were related in someway. Dr J. W. McCrindle and Dr H. R. Gupta think that they both possibly belonged two different branches of the Ashvakas
Source: Invasion of Alexander, 2nd Ed, p 112, Dr J. W. McCrindle; Op cit., p 33, Dr H. R. Gupta; Dr McCrindle further writes that modern Afghanistan was the ancient Kamboja and that the name Afghanistan is evidently derived from the Ashvakas or Assakenois of Arrian See: Megasthenes and Arrian, p 180; Alexander's Invasion of India, p 38; Dr J. C. Vidyalankar identifies Sisicottos as a Kamboja ruler: See Itihaas Parvesh, pp 133-34, Dr J. C. Vidyalankar; Kamboj Itihaas, 1973, p 58-59, H. S. Thind.
Meri was probably another political centre of the Mor or Meros people. It is asserted by scholars of this school that the name Moriya or Maurya comes from the Mor (Modern name Koh-i-Mor i.e Mor hill---the ancient Meros of the classical writings) located in the Paropamisade region between river Kunar and Swat in the land of Ashvakas (q.v.). It is pointed out that since Chandragupta Maurya belonged to Mor (Meros of classical writings) hence he was called Moriya or Maurya after his motherland.
Source : Op. cit., pp 32-35, Dr H. C. Gupta; Also: The Kambojas Through the Ages, 2005, pp 149-154.
Tribune writes: "Most historians are of the view that Chandragupta Maurya belonged to Bihar, and that he called himself Maurya because his mother was the keeper of royal peacocks (mor) at Pataliputra. He came to Punjab and conquered it. Afterwards, with the help of the Punjab army he seized the Nanda empire. However, there are reasons to believe that Chandragupta belonged to the Kshatriya caste of the ruling Ashvaka tribe of the Koh-i-Mor territory. He called himself Maurya after his homeland" (Ref: Article in Sunday Tribune, January 10, 1999 They taught lessons to kings, Gur Rattan Pal Singh; Also cf: Was Chandragupta Maurya a Punjabi?, Punjab History Conference, Second Session, Oct 28-30, 1966, Punjabi University Patiala, p 33, Dr H. R. Gupta)
It is notable that Adiparva of Mahabharata (verses 1/67/13-14) also seem to connect Maurya Ashoka with the Ashvakas
Source: yastvashva iti vikhyAtaH shrImAnAsInmahAsuraH |. Ashoko nAma rAjAsInmahAvIryaparAkramaH. ||14|| tasmAdavarajo yastu rAjannashvapatiH smR^itaH |. daiteyaH so.abhavadrAjA hArdikyo manujarShabhaH ||15.|| ( See English Translation): "That great Asura who was known as Aswa became on earth the monarch Asoka of exceeding energy and invincible in battle."
Dr Spooner observes: "After Alexander's death, when Chandragupta marched on Magadha, it was with largely the Persian army (Shaka-Yavana-Kamboja-Parasika-Bahlika) that he won the throne of India. The testimony of the Mudrarakshasa is explicit on this point, and we have no reason to doubt its accuracy in matter of this kind".
Source: op cit., (Part II), p.416-17, Dr D. B. Spooner Thus, Dr Spooner's comments also point to the north-western origin of the Mauryas.
It is however interesting to see that the scholars also identify the Ashvakas as a branch of the Kambojas. They were so-called since they were specialised in horse-profession and their services as cavalrymen were frequently requisitioned in ancient wars. V. R. Ramachandra Dikshitar writes: "Both the Puranas and the epics agree that the horses of the Sindhu and Kamboja regions were of the finest breed, and that the services of the Kambojas as cavalry troopers were requisitioned in ancient wars
Source: War in Ancient India‎, 1944, p 178, V. R. Ramachandra Dikshitar - Military art and science.