It's a business to them and not many business have no debt. It's a means of earning money for them, nothing more. They do that very well apparently. Keeping to that is much better than insisting on buying players the manager doesn't want as some owners seem to do.
So far, and it does seem to be so, SAF has got all the money he has asked for. Whether he has used that wisely is debateable. If you don't think he has you cannot blame the Glazers. If you think he has, then well done the Glazers for allowing him to do so.
Just think anyone of you guys could also have bought United for nothing if you knew how to. The Glazers obviously did.