While there was a Hi-Po version of the Quad-4, there was also a standard SOHC version that was the base engine in a bunch of GMs in the late '80s/early '90s, and then a milder DOHC version became the base engine in cars like the Malibu all the way up until the Ecotec in '03 or so. The problem was that even in the base engine, NVH sucked (it was bad in the Hi-Po versions too) and people still didn't accept 4-cylinders in the downsized American cars of the 80s/90s.Also, the 3.4s (both the quad-cam and pushrod versions) and the Iron Duke/Tech 4 must be worse. Although generally reliable if you could keep enough oil in them, the 2.5s were underpowered, thirsty and GM's refusal to develop a volume OHC four in the 1980s was to the company's detriment.
(Yes I'm aware fo the Quad-4 but that was a rare performance engine)
But to GM's credit, getting 150-180 hp from a N/A 4-cylinder in the '80s (190 hp in the '90s) was impressive. But the characteristics people cared about in '90s GM cars were really not the Quad-4's strong suit, and the cars they were fitted to were similarly lackluster so it was largely ignored.
So I disagree that GM refused to deliver a volume OHC 4, since the Quad-4 had a good 15-year run, and it is decidedly NOT rare -- well, might be rarer today since most of the vehicles it was put in ended up in the junkyard after no one wanted them, but they were fitted to a lot of vehicles from the 80s/90s like the non-SCX Achieva (SCX got the top dog 190-hp DOHC motor) and survived in the N-bodies (Malibu, Grand Am, Alero) into '03. It's similar to the story of the non-turbo Ecotec motors, they're fine from a technical and reliability perspective, but the cars they got hitched to were not that impressive. It actually makes a pretty decent swap engine into a Miata