Because it's faster and flies higher than M-346. It can fire real weapons too, unlike M-346.
It will come within 90% of an F-16 Block 52's flying profile with the upgraded F414 engine.
Assuming Israel has money. They are actually short on cash.
How high would T-50 want to fly about, what an unprofessional statement, M-346 has a credible profile and has gone through several Tests including weapons Testing that is why different variants are officially on offer.
Here a link M-346 has even Tested medium range light weight antiship missiles, So Yes real weapons are Tested-Fired including A2A and A2G and antiship..
http://www.mbda-systems.com/mediagallery/files/marte_mk2_A_ds.pdf
Hardpoints: Provisions provided for a total of 9 pylon stations (2× wingtip, 1× under-fuselage plus 6× underwing), capable of mounting up to 3,000 kilograms (6,600 lb) of external payload and up to 3× 630 litres (140 imp gal; 170 US gal) external drop tanks (only pylon stations 4, 5, 6 are wet-plumbed)
mixed load of all types of Russian and western air to air (short to medium range) and air to ground dumb and smart bombs.
Israelis are buying M-346 according to their requirements, no need to flairup, T-50 is US product with s. korean stamp, at this point of time the most successful next generation design is M-346/YAK-130 that offers good enough similar to what T-50 is offering. Even if you declare it more Taiwanese design-input remember FCK-1 was designed with assistance of US, sorry man you info is wrong. But T-50 has its own profile and M-346/YAK-130 has its own operators would procure it according to their needs, if it is rejected it is rejected for a reason.
Please, it will never come with-in even 50% of F-16 block 52 profile, US will never allow it, trainer is trainer will be.
Actually isrealis are not short on cash I can list you fortune 500 companies along with famous isreali jewish belonging multibillion dollars companies many of them belong to isreali entrepreneur-businssmen-isreali citizens.