I think it isn't quite so clear-cut. As usual, there are two sides to the story.
Some manufacturers may have lowered their standards in the eighties, in order to cut costs when a new, shinier star was born. But on the other hand, back then there were hundreds of them, catering to an enormous audience, 90% of which were playing their records on cheap, crappy turntables and couldn't have cared less about sound quality (as long as it was at least minimally better than AM radio, that is). The bar was quite low. Despite what our fading, selective memory is telling us, the quality of the pressings used to be all over the place, even though most people didn't notice at the time because they had nothing better to compare it with.
Actually, some people
did notice. Many rushed to embrace the new medium, despite its initial flaws and higher cost, precisely to get rid of the bad sound of the LPs of the time.
Nowadays the LP market is aimed at a handful of hobbyists who know their stuff and use high quality gear. Consequently, the very few remaining manufacturers cannot afford to be as sloppy as they were in the past. They need to pay close attention to details, because what used to be acceptable in the seventies and eighties wouldn't cut the mustard today. Back then they used to press an awful lot of LPs from one master lacquer, to increase productivity and keep costs low. They don't do this anymore. They used to melt unsold records and recycle the vinyl. Today they use virgin vinyl, and of better quality to boot.
Leaving aside the mastering differences, which are mostly a matter of taste anyway, the sound quality has improved massively. The LPs pressed by Deutsche Grammophon today that I have in my collection sound way, way better than the ones from my childhood. Considering only the technical quality of the sound, the "roundness" of the sound, the harmonics, the fullness and cleanliness of the bass, the noise floor, the imaging, they are virtually indistinguishable from CDs, which is emphatically not the case with my older ones.
Sure, there is the odd defect here and there, like a scratch or a fingerprint, but this isn't a new phenomenon. Old LPs used to have them occasionally, too. It's just that back then they were perhaps less obvious because of the sheer volume. One defective record in ten thousand is less visible than one in a hundred. Back then you went to a music shop and picked one copy from a stack of ten. The chances of your picking the defective one were slim. Now there's only one copy in the store. If that happens to be defective, tough luck.
But I'm awfully off-topic. Sorry about that. Let's go back to cleaning.

... though when it comes to cleaning, there's only one thing to be said - ultrasonic rules. Period.
