Ok, you seem to be missing this factor in all of your arguments.
The currencies of all the countries you mentioned trade very unfavorably (maybe not the right word) with respect to the USD. So even if the cost of a higher ed degree seems like a lot to US locals, that cost is a few orders of magnitude higher from the perspective of a family considering this investment for their ward.
The only way this degree is worth the money, even after the substantial scholarship/assistance that US schools used to offer, is if you got a job that pays you is US Dollars. If at the end you don't get such a job, then the degree isn't worth the paper it's printed on.
A masters degree used to cost about 20-30 thousand dollars in total if you got the aforementioned scholarships/assistance. Then once you landed a tech job you'd have made up your original investment within a year if you lived frugally, which most international students tend to anyway.
After that you could save up your money, which would be a substantial amount once exchanged for the local currency and return. This is unlikely.
Because most would choose to stay and climb higher on their career ladder and provide a more luxurious standard of living for their families.
This is the whole point of going through the university system, not the degree.