There's plenty of chubby guys that like slim dudes, trust me, I consider it a problem(Chubby/fat person here), since I'm chub4chub.
If you're looking for a relationship, it mostly depends on your personality, if you're all up and about telling guys you'd bang them, and greeting them in a way that more than likely puts them off, then that's probably why, unless you haven't, then they're possibly just not into fit guys.(And are scared of saying so, that, or maybe you didn't read their profile carefully? Idk)

Reason why I'm chub4chub is because of the massive amount of fit/skinny guys I've had send me messages where they tell me I'm cute, then stop talking for good, or just end up saying something silly like "I'd love to screw the hell out of you."(It's good to know, but some guys might think that's weird/unnecessary to start a conversation with) Along with the fact that I was bullied most of the time by skinny people, so I sort of just stayed away from them, and chose to like bigger guys like myself.
There's plenty of reasons a person might not reply to you, but I'm 100% certain there's plenty of chubby dudes out there who dig fit dudes.
Chasabl is certainly a place you'd want to try out, as I've been on there for a few years before, and basically there's plenty of bigger guys whining about not having a skinny/slim/fit guy to love, so you'd probably have a bigger chance there.

Now, saying all this, this doesn't mean I'm an expert or anything, this is all just from my experience.