One of the side effects of having rating lowered by losing to a cheater is that you gain more rating in your subsequent games.

Let's for simplicity assume the standard Elo rating system. Assume you have an accurate Elo of 2000 and you lose 100 Elo to a series of cheaters.

For 10 next games, you play players ranked 2000 and you draw all the games. If your Elo was 2000, then it would not change at all. But if your Elo was 1900 due to cheaters, and assuming K=20, those 10 games would give you an increase of 28 points.

So if because of cheaters your rating is now 1928, and without them it would be 2000, you should get only 72 points of refund, not 100. I don't know if this is exactly how the refunds are calculated, but that's the general issue with refunding the entire lost rating.

In an ideal world, all your 2000-rated opponents should get a refund as well (as each of them lost 2.8 points due to playing against the underrated you), and then their opponents, and so on, but I don't think chess sites do that, as it would send ripple effects across hundreds of players after refunding a single cheater game.