Using those traditional free CAs still required getting the signed certs through a sometimes obscure process from their website, transferring it manually to the target system etc.
The manual handling alone, which causes work, adds another point of possibly exposing secrets, does not scale, can't be automated, etc was reason enough to replace it with ACME, even if setting it up would be quite complex (which it isn't at all).
There were some fairly grave noob-type security bugs in that service (to be fair Let's Encrypt almost went live with a fairly grave but more subtle to understand bug, and did go live with tls-sni-01 which it turns out is unsafe if people use Apache HTTPD for bulk web hosting which er, they do). Because of the grave problems StarCom turned their API off after not very long, presumably with the intent to eventually repair it and re-launch.
A surprising number of people became convinced Let's Encrypt was some sort of attack on StartCom and that the other problems with StartCom/ WoSign (eventually leading to them being distrusted) were a conspiracy to popularize Let's Encrypt.
Automation solves these problems. Don't be the computer's slave--tell it what to do.
2) 20 years' expiration is a security risk that should not be taken. Letting you do that would be a bad idea not just for you--you can make stupid decisions on your own--but for anyone who connects to you, and you aren't entitled to do that.
I don't understand why someone who is theoretically a programmer would be so odd about this.