No, it's because they are extremely unhappy with themselves and would love to change their lives, but can't find the beginning (trapped in their pathetic day to day family/job lives). So they try to put people they envy down to make themseves feel better, instead of changing their own lives.
since when being muscular makes you "happier" than them. It may make you healthier, but psychologically happier? 2 different things.
Never forget these people might feel happier than you even with an out of shape body. If muscles= hapiness and if more muscles = more hapiness i think we would know

seeing so many obsessive losers pathetically showing off in the gym -the only place where they are respected for their endeavours- and everywhere they go only proves they re as insecure now whatever the "muscle mass" they achieved as when they started lifting weights.
Just believing that because you have some muscle = you re the happiest/better person than other people who arent as "inshape" as you is a common yet stupid mistake.
Btw your level of "hapiness" is mainly linked to your serotonine levels, it means it's essentially genetically programed.