Why are humans so complicated?

A friend of mine for around 4-5 years at this point has randomly started ghosting me completely over the past month or so... I know they've seen my messages and I know that they're also autistic so they'd know I probably wouldn't get it and I saw no signs of the friendship having any problems and yet they've just suddenly stopped and I have no idea what I did wrong...

Why is being a functioning social creature so damn hard?