Of course it's because he's gay. Also many gay men (not all) are much slimmer, fitter, healthier and better dressed and better off than straight men of the same age and seek a certain visual aesthetic which your average fat ugly bald middle aged/older British man long since abandoned.
We need many more pictures of older men. This is good one.
Sewell entitled to his views of course. We could make a modern art work - it would consist of the portrait in the middle, Sewells words across it and a naked Sewell with a gorgeous 25 year old young male lover. I haven't quite worked out where that would go.
We have his father, Peter Warlock, however to thank for some wonderful pieces, which I expect a lot of us and our children sing, particularly Christmas -