Hi OP, you're of course right and I don't have much to add to other posters in terms of this particular situation.
But you mentioned not being able to work him out (an exaggeration after all these years, I'm sure!) but it strikes me from what you've that the common thread is that he is very much a 100% person and absolutely, viscerally, can't do things by halves.
Work - all consuming, 7 days per week, must continue until he's 70 (hence as you say, no bandwidth for much else). You - best friend, wonderful person, no need for anyone else. When he does go out - life and soul, last to leave. Guests - must (in his mind) be fully acknowledged, hosted, attended to- not to do so would be "rude" of him and embarrassing you in some way (so anywhere he is in the house while your friends are over, his peace is 'destroyed')
That all fits with his father's attitude that life is for hard work, doing your best etc.
None of that means you shouldn't have them round - absolutely not - but that's my speculation about what's going on here. It sounds like a deep-rooted approach to life and sense of what's right and owed from him to other people/ things. If he's going to do something, he had to throw himself into it 100% and do it with total commitment.
That's also a wonderful quality in many respects but had its drawbacks!
Just in case that rings true and helps you plan an approach to this.
Maybe making up some nonsense about how friend X, Y or Z who is coming over had said to you that she knows how hard your husband works and hopes he doesn't feel the need to get up and play host while they're all there / that they'd feel much better about being there if they knew all be was going to do was pop his head in and then retire might help give him "permission" in his own mind?