From a HR perspective, to get rid of Sancho it would be very easy to terminate his contract, without pay, if he's had warnings, been late, been disruptive in work, not met performance criteria etc. Nobody is getting a 350k a week contract nowadays without there being some protections to the club, if he's acting like a tosser etc.
As for Greenwood, it's a bit of a different situation, as I presume he was a "normal pro" with regards for turning up for training, on time, not being disruptive to the club etc, actual job related things. It would be harder to fire someone for something they do in their personal life, if they've been good in their pro life. Then as for Greenwood, as the proceedings were dropped, his name is effectively clear in the eye of the law, which means Man Utd would struggle to sack him without having to pay compensation. What he did was wrong of course, and morally very bad for the club, but they couldn't go after him from bringing the club into disrepute, until he was actually convicted, which he wasn't.
This above doesn't mean that Sancho/ Greenwood are worse in different ways, but seems like Sancho is a poor performer, and a crap pro, so probably a tosser in his personal life too, but Greenwood is effectively an unconverted criminal which is obviously worse than anything Sancho did, but from a HR point it's likely untouchable.
Greenwood has benefitted massively from the effective "innocent until proven guilty" law, which wasn't really designed to help criminals get off, or get their cases quashed/ paid off, it was more about protecting people who wouldn't actually be found guilty, usually as they had done nothing wrong (which doesn't seem to apply here, as per the evidence).
Morally, Man Utd could not have terminated his contract, but they could have paid his contract up and released him, but this could be seen by many as a reward, as he could basically then go to another club, sign another contract and basically get double pay. It's a difficult situation for them, no real win, so maybe it is best to let his contract run out, with pay, and have some other club pay his wages to man u (or maybe they're not even paying his wages). He won't get another Man U contract, and won't ever end up on the pay he could have had, had this not happened etc, so it's the only way he can get punished, and seems Man U's only real route out, without the player benefitting more than they should or could under protection of UK law.