They aren't. Tel wasn't their #1 choice according to Plettenberg; they had a more experienced option ahead of him (Nkunku, possibly). INEOS, however, want to make a profit on every possible incoming transaction, so even if United's revenues are decent, they don't want do spend more on their total incomings than their total outgoings. This is how INEOS operate their other clubs like Lausanne and Nice. They seem to use PSR as a reason for not being able to spend more, but that seems more like a convenient excuse for them in their chase of profiting off of United's transfers. I say this because they're no longer paying as much in the salaries of the players that they loaned out, and the players they brought in this month aren't likely to be on big contracts, either.
They want to grow their profits so that their shares appreciate in value. I wouldn't be surprised if, in the summer, the same narratives come out about having to sell before they can buy more players.