Also many companies got burned thinking the smorgasbord of free traffic on social platforms would never end.
It turns out that when your primary business model is selling traffic (via ads), giving it away for free is antithetical to your margins.
Facebook, Twitter, Instagram, and TikTok (sometime soon) started off giving creators (and businesses) tons of free traffic only to eventually suppress it to push people towards paying to reach the followers they worked so hard to get.
On the other hand, once someone has given you permission to email them then it really doesn’t matter if you do it from your own mailserver, mailchimp, or anything else… They are still expecting you to be in their inbox (hopefully delivering great value).
Source: I was reading the internal newsletter in the bathroom of a major social network's office ~6 years ago when they were announcing (in celebration) that they had suppressed organic reach to sub 5%