Most streaming services have introduced cheaper “ad-supported” tiers within the last few years while jacking up the prices of the existing tiers. There is usually a price gap designed to either make you sit through ads or overpay to remove them. Many (most?) people don’t even use ad-blockers in their web browsers and are psychologically trained to sit through ad breaks, either because of TV (older generation) or YouTube (younger generation) which is why these streaming companies can get away with such a betrayal of their original premise.
Resolution doesn’t mean much, those sites you are referring to use extremely low bitrate encodes that look terrible. Yes, streaming services (in my experience Netflix is the main offender) can sometimes deliver dogshit quality streams too due to their adaptive bit rates, but the ceiling is way higher than those sites that pull from DDL file hosters. If you are consistently suffering from very low quality paid streams then you likely have some kind of network issue affecting the adaptive bitrate.