(This is basically my response to the earlier post asking why this was, but by the time I saw it it was 10 hours old)
Now I'm not saying bike bad or that they make you look like a loser or anything, just that typically they don't make someone look especially those descriptors above.
Realistically, in an IRL apocalypse? Yeah, odds are there'd totally be way more people using bikes to get around than stuff like horses.
In fiction tho? What's scarier: A pack of raiders coming at you on horseback, or a pack of raiders coming at you on bikes like a 50s gang of middle school bullies?
spoiler
(It could also partly be a subconscious thing since, in the U.S. at least where most media is created, bikes are associated more with children/adolescents and athletes than "normal" adults, and is not usually thought of as a "normal" means of regular transportation.)
(And just to clarify: The tone I'm going for with this post is a fun, non-serious one, not an angry, argumentative one.)
At least in the US. In other countries where bikes are more commonly used by regular people I'm sure their fiction reflects that more.