Some bettas just don't bubble nest, or only make very tiny, poorly put-together nests that dissolve apart before they start to look like anything. Much like people, some bettas are very macho with a high sex drive, and others aren't. You might just have a gentle-natured or immature male who isn't interested in building a nest for a potential mate. It is equally possible that captive breeding over many years have "watered down" his instinct to do so.
I have a male who is over a year old. He is active, healthy, aggressive, eats well, has plenty of space, and he has never built a bubblenest. He sometimes blows bubbles on the edge of the tank, but never builds a real nest. I assume that it is just part of his personality.
I don't believe that bubblenests are necesarrily a sign of health and contentment. I had a betta who was dying of dropsy who made an absolutely massive nest. And I've seen bettas in cups so tiny, dirty, and cramped that they can hardly breath, and many of them have nests even then. I think it more depends on a desire to breed, which is why we see increased bubblenesting in males exposed to females, or conditions similar to breeding season in their natural habitat (ie. shallow still water, humid air, warm temp, etc)