That's only because at the time ABC was the only game in town: Armalite, Bushmaster, and Colt. DPMS, SGW, some other smaller companies made some stuff here and there, but they were pulling shenanigans like cast (vs forged) lowers. Colt was mostly unobtanium in the civilian market and when you got them they had neutered carriers, oversized FCG pins, sear blocks, etc.
Bushmaster has never made a "good" rifle. It's just they were the best of what was available. Most of the issues are correctable with proper tools, knowledge and parts. The biggest parts issues are gas port size on barrels (too large), buffer weight (exacerbated by over-sized gas ports), gas key screws, and receiver extensions (buffer tubes).
All that said, if in-spec, (and from what I've seen they usually are; certainly more than RRA) the OP will be fine building on a Bushmaster lower.