@royblizzard I think you are stuck between battling issues or insecurities so you might need to look in specific pools. I am hopelessly mixing my metaphors. Sorry.
You are muscular and strong that makes a certain type of guy insecure (small minded ones). They don't want to feel small or be the butt of jokes that you can bench press them and beat them up. Which you probably can, and with your military background probably could have done well before CF.
Think about how some (lots of) tall women don't want to date shorter men....it's a cliche because it is accurate often enough. Similar if opposite insecurities.
If it is any consolation it does happen to some guys too. Lots of girls like the idea of a muscular man, will hook up briefly with them but when a) he spends all his time in the gym and b) watches what he eats all the time and c) he makes them feel slightly more insecure in a bikini and they don't want the added pressure of trying to be lean too....same outcome.
On the plus side. You are strong, dedicated, disciplined and fit. There are millions of guys out there who will be very keen on that. Maybe you just have grown out of the pools you used to be looking in.
39 and 40s is tough for dating, tough for platonic friendships too. Lots of people are in relationships and doing other things. Change tactics but sounds like you have lots of assets, no problem.