Earlier quoted context omitted.
There's also M.2 "M key" and M.2 "B key" because why not have two different types of connector in your brand new standard. There's also "M+B" which reminds me of the days of CD-RW and CD+RW with CD+/-RW thrown in to try and unify things. https://en.wikipedia.org/wiki/M.2 This is annoying because some dual M.2 adapter cards have one of each, so you can't use two M-type cards in it.
Because this fixes the issue of "i plugged it in but it doesnt work" issue, as you already know it wont work because it doesnt fit. Kinda like DDR slots
I can't think of another standard made so deliberately difficult to install. A distant second is the 6/8 conductor PCIe power connectors that are a giant pain to use. Why couldn't they just force 8 for everyone and be done with it? Instead we have these crappy split connectors.