Design "errors" in Xanathar's

[Dr. Cliché]

One of the biggest points of confusion in the design of 5e for me is why they took away Eldritch Blast as a Warlock class ability and made it a cantrip. What were they trying to achieve?

Well, I don't necessarily mind it being a Cantrip for simplicity purposes, though it does seem a bit weird that other classes can learn it without making a pact themselves.

Bard - "So, how did you learn Eldritch Blast?"
Warlock - "I pledged my very soul to Asmodeus, Lord of Devils!"
Bard - "Oh, that's cool I guess. I just learned it while playing music."
Warlock - "..."

As I said though, I think the stranger aspect is that they made it an optional cantrip. What exactly is the benefit of not taking the best damage cantrip in the game?

Also, on a more personal note, I really miss some of the upgrades to Eldritch Blast that you could get in 3.5. I loved Eldritch Chain, where you could have it arc from one enemy to another. I also liked Vitriolic Blast.