To be having this sort of conversation you'd have to bring in old timers, too. You can't have people that have not lived through the 70s and 80s to be dissecting this matter. By living those time I mean to have actually been going to football matches and so on, it would have to be people in their mid 50s now, early 60s. How many are in here? Don't think that much to be fair.
Genuine question though? Do you think Liverpool was winning so much back then being on par with the others? Do you think their budget was the same as Chelsea's? Salary wise, transfer wise etc? You'd have to be a fool and born post 1990 to think Chelsea was not massively represented in England. What Liverpool and others had back than was a powerful backing, something you see now with City, PSG, Chelsea etc. There was always a wealthy family/business/figure behind every successful project. Always.
'Plastic', 'Oil money' etc. Terms used by kids that have only watched football post 2000. Ask you grandfathers they will tell you it's a normal thing for winning teams to be the wealthiest around, Liverpool did not operate on peanuts money in the 70s and the 80s, nor was United during their glory days, they were a different animal from the others in terms of money spent on transfers and contracts.
Stop fooling yourselves Liverpool and United went from average spending to being wealthy just by having a good fan base and global recognition. It's a foolish thing to do, better ask your old pals and then maybe all the bs would stop.