I’m pretty sure that it wasn’t Windows that was the main offender, but instead legacy systems of all kinds made since 1970, where people were not expecting for their programs to run for more than 30 years.
Surprise! Businesses don’t care whether the code is old, as long as it works - so that data type you store the year in only held two characters, and hard-coded the 19 onto it.
1999 would be written as 99. 19 + 99 = 1999 = computers were happy.
2000 would be written as 00. 19 + 00 = 1900 = computers went to shit