I don't think that it has anything to do with social stigma here.
Condoms are almost available everywhere, and you can even buy some without having to interract with another human. And even if it's not free yet, it's cheap.

One thing i noticed (i think) is that younger people are not scared by STDs the same way older people were.
Catching an STD is kinda rare here, and for the last 50 years it has been more and more uncommon.
And because of that i think that younger generations aren't scared about STDs or Aids the way older generations were. And therefore, take less precautions when engaging in sexual intercourses with others.