That is obviously also gonna be a reason. But I could imagine that his staff feels more comfortable with Schengen as a zone with (usually) open borders and high infection rates rather than specifying single countries. The latter would probably be harder to keep up in courts.

FWIW, without making this political, I don't even think it's the golf resorts. US and UK have very close economical links, there's a lot of business traffic. Esp by wealthy people flying NYC-London regularly. I would rather think he didn't want to affect those. I can imagine a lot of his friends would've been angry if NYC-London gets shut down. Most visitors to his resorts in Europe will be from the continent anyway. But that's obviously pure speculation.