Why is that some men in their 30s and 40s are so into the gym?

This was a comment I had on another thread but I decided to make it its own. I am not trying to bash the gym but I personally know of a lot of men who get so focused on the gym. A lot of the time I notice they put it way up to a high level of importance which is why it baffles me. I could care less if they are very fit but it becomes weird to me when they focus so much on it. I’ve heard them talk about what they ate, how they squeezed their muscles harder, this that and the other. I am not sure if it’s a cultural thing but I don’t understand why it is so important to them. Also feel free to share your thoughts and experiences.