Whatever you think of the players individually, selling so many in one summer would be undoubtedly destabilising. Not every player they have wanted sold necessarily has a long-term future at the club, but it would be an horrendous decision to get rid of everyone they listed in one summer. You'd need to spend much of preparation for the new season working to mitigate the massive unnecessary shock you've just inflicted to the culture of the dressing room. Get rid of a few but we can't sell so many players that those that are left are going to notice a draft. There'll be personalities, characters that might not belong to someone you want to give a contract extension to, but you need to be strategic about when you move players on you can't just have a cull every summer, not if you're looking to build something.
Especially where we are at the moment if everyone turns up in July to find out half their team mates have been sold I don't think it's going to do much to ensure we get off to the best of starts. You need to be strategic with these things and often the decisions aren't just about football. Wrecking the morale of a squad because you've identified 1/3 of the team probably aren't of the calibre you're looking for in the long run would be a terrible short sighted decision. You need to churn them out strategically over a few cycles.