Anybody knows why tax forms from investing platforms like etrade, vanguard, etc. take more than 45 days to be sent?

There are some tax laws that require at least 30 days, like Wash Sale rules for stocks. It means for many people they literally cannot issue the forms before Jan 31st. I think the forms are due Feb 15th, which gives them 2 weeks. It makes that companies have at least SOME time to generate (2 weeks). I don't know why they don't generate forms earlier though when they know it's possible.

Because things can change based on EOY status for companies, like dividend payouts, and they don’t want to issue too soon and then have to reissue.

To determine wash sale they need to wait until Jan 31 for stocks you could have sold on Dec 31 but re bought on Jan 31st.