You are welcome. But I have to remind you of a little invention called Google. There curious questions such as the one you asked can be answered.
You live in Bangladesh. How many Saudi Arabians do you see in Bangladesh? Have you been to KSA?Let me remind you of the fact that nearly 50.000 Saudi Arabians study in the USA alone. Only Chinese, Indians and South Koreans have more foreign students in the USA than Saudi Arabians. We have the most per capita by far. Do you think that they all wear traditional clothes? I don't believe that more than very few do it. Because it would like out of the place. Likewise foreigners who are studying or living in the USA are not going around in traditional Indian, Bengali, African etc. clothing for the very same reason.
Anyway now you have seen some not wearing traditional clothing:
Anyway what is so special about wearing jeans and t-shirt? I think that Arab traditional clothing is much more beautiful and diverse than simple jeans and t-shirts. We stick to our own culture, traditions, religion etc. Always done that.
People do not wear Burqas in KSA. Only normal headscarfs or a niqab if they are traditional. It depends on the region/province of KSA and city. A abaya is worn by nearly all in public though but a headscarf is not obligatory. For example you will see tourists/visitors not wearing a headscarf but a abaya instead.