Why do many of them have different feed lips and followers?
Followers -
Initially, it was probably to squeeze an 8th round into a tube designed for 7 rounds. Now, it's probably mostly marketing. " Here is our new and improved follower...", though I suspect some of it may be ease of manufacture for a follower design.
This thread has some follower discussion (
https://www.thehighroad.org/index.php?threads/1911-mag-follower.868578/#post-11504836 ), and at post #23
SSN Vet has picture of some common followers. The Metalform follower, second from the bottom on the right is commonly called the "GI" follower. It is the original John Browning design, but you can't use that follower and get 8 in a tube designed for 7.
Feed Lips -
The original Browning design had tapered feed lips, now commonly called GI feed lips. They work great will ball ammo, especially 230 gr ball. Outside of China and third world production, there aren't many companies still making this design. I know CheckMate does, and probably Metalform.
Nearly all current manufacture 1911 mags have wadcutter feed lips. They showed up in probably the 1970's as a way to get short rounds like those with semi-wadcutter bullets to feed better. Since most hollow point ammo is also relatively short, they also work well with self defense ammo. They also work with ball ammo, though not as smoothly as GI feed lips, so they became the manufacturer default design. I suspect their simple shape also makes manufacturing easier.
Hybrid feed lips are a Colt design from probably the 1980's. They are a compromise between GI and wadcutter feed lips. They feed relatively smoothly with ball ammo like GI feed lipped mags, and they also feed short rounds like wadcutter's and hollow points. I believe they are currently only offered by CheckMate, though Metalform did make them in the past.