USB-C's ecosystem was confusing and good products never materialized, or if they did nobody could find them in the sea of junk.
The lack of hardware updates, which seems to have started with the 5-10% performance bumps Intel piddled out in the absence of competition from AMD from 2011-2017. Most of the CPU's and GPU's that could have been used frankly weren't much better than what they'd replace, so from that standpoint, upgrading the hardware was kind of pointless for an extremely minor performance benefit.
The keyboards situation is horrible. Failure prone and loud without much point.
Apple is making a lot of money in the iOS ecosystem. Success hides problems, and it seems like "if it's not broken, don't fix it" was used as an excuse to let the Mac languish.
As someone who did nearly all of Apple's IT-related certs in the mid 00's then watched them slowly decontent and destroy all of their OS X Server and related software almost immediately as iOS was on the rise, I don't see good things coming on the horizon.
If you're on a Mac, try to start using primarily OSS software and. Don't get stuck on a platform that might get abandoned tied to a workflow on software that isn't portable.
The silly thing is that Apple could (and should) invest in the Mac as it was pretty great, and could be great again. I'm not holding my breath.