Well they had to to a point, didn't they?
Becks had two years left on his deal (I think) and wasn't in a rush to sign a new one. He was 28 so at peak value, only going one way from there. If he'd stayed, Ronaldo was hardly ever going to play - not that he actually did play that much in his first season, as we've seen. Given values at the time, it was a good price from Real. Worked for everyone.
Not a straight either/or choice but if you view Ronaldo as a generational talent - which he obviously did end up being, in fact becoming a world legend, and eventually he and United had a seriously golden period together - then you'd remove a fairly obvious bar to him getting gametime. Unless you think Fergie would have sat England's captain, their primary provider of assists and one of the world's most famous people on the bench for an entire season for an unknown, hit and miss 18 year old at the time...
In the same way we haven't directly moved Jota on to fund Fabio, but it's all part of the bigger picture. If he's here and available then Raul being fit or not, Fabio is hardly going to play.