That's the problem though isn't it. IMO the sensible thing to do is to bank a fair proportion of that money for the future and not take on massive financial risks and commitments, but relegation is pretty much assured within a season or two and then the fans and pundits are saying "they didn't invest" and you've got fans on the teams and managers back and calling for you to sell the club, creating a negative mindset around the club and potentially starting a losing mentality and spiral of decline. The PL also don't want that because as you said it affects the product.
Or you spend it on big transfer fees and wages (often on quite mediocre players) in the hope you'll stay up, just to have to go through the same thing again year after year until inevitably one year if fails. Then you're relegated with almost no financial buffer and big spending commitments on transfers and salaries in the future, creating an added financial problem on top of the problems on the pitch exacerbated by the fire sale of high earners and sale of good players to meet those commitments. PL much prefer this because their product remains high but when it goes wrong you're an EFL club who's spent beyond their means, not a PL one. Never acknowledging that the reason they spent beyond their means in the first place was because they got to the PL and were almost forced into doing so, spending tens of millions on Jorge Mediocre and Jose Average on over a hundred grand a week.