Bluetooth is massively more complicated than WiFi. It has a whole service enumeration/discovery layer baked in that IMHO tried to cram way too much into the spec. Whats even more amazing is that some of the hardware vendors at the table during the development went "F that" and added some side channel audio stuff that bypassing most of the stack.

But mostly the problem is that too much of this complexity fell on hardware vendors and they suck at writing software. There are umpteen bajillion different bluetooth stacks out there and they're all buggy in new and exciting ways. Interoperability testing is hugely neglected by most vendors. The times where Bluetooth works well are typically where the same vendor controls both ends of the link, like Airpods on an iPhone.

In 2020 I tried buying some reputable brand Bluetooth headphones for my kids so they could do home-schooling without disturbing each other. It was a total failure. Every time their computer went to sleep the bluetooth stack would become out of sync and attempts to reconnect would result in just "error connecting" messages, requiring you to fully delete the bluetooth device on the Windows side and redo the entire discovery/association/connection from scratch. The bluetooth stack on Windows would crash halfway through the association process about half of the time forcing you to reboot the computer to start over. Absolutely unusable. I tried the same headphones on a Linux host and they worked slightly better, but were still prone to getting out of sync and requiring a full "forget this device" and add it again cycle every few days for no apparent reason.