Simple answer is...they're not all so buggy. Back when I was working for a client that had AirPort Extreme's hardwired around the office, I was constantly having to reboot them as they would stop working and a reboot was the fix. Finally replaced with non-Apple gear and problem solved.
Nowadays, there are plenty of great mesh systems available, and you don't have to spend a mint to get fast, reliable performance. In my home and about half dozen clients offices and homes, I've put the TP-Link Deco X60 mesh system. Hardwired all X60's when possible (like in my own home). Absolutely flawless. Easily 600-700 down and great reach out to the patio and typically on sale for under $200 for a 3-unit pack. I would never spend top-dollar for some of these companies high-end gear. I have to look twice sometimes at the price tag for some of these mesh systems.
The WIFI market is saturated. Apple can't get any traction in a market with so much competing product already. They'd have to have a trick up their sleeve, different from everyone else, and we know Apple isn't so much into that these days and if they were, it'd take them 3-4 years to release it (after a handful of delays).