TCM was available (alongside all of Warner Bros. Media, Turner Media and DC Comics)... It's getting absorbed by Discovery [1], I imagine that a competitive bidding process must have taken place, presumably Netflix didn't see the benefits.
[1] https://www.cnbc.com/2021/05/24/john-malone-sees-warnermedia...
I'm with you on the old black/white movies.
I actually think Amazon got a great deal buying MGM.
If TCM was available, Nefflix should look into buying it. They have a great library of old movies.