Hosting can be free if you use your own server, it is the bandwidth, the actual internet connection that costs money.
As someone in IT, I can tell that you don't know what you're talking about if you think running your own servers (note: plural) is anywhere near "free". This isn't some random spare old machine someone threw Apache on and stuck in a closet. You have the cost of the servers, replacement servers for when they reach end of life, maintenance contracts, replacement parts when things like hard drives fail, SAN storage and networking gear, and license costs (just to name a few), none of which are remotely cheap let alone "free".
And they make more in advertising than you would think.
Considering that appears to be their profit model, what's your point? That they're a successful business?
Well here is a list of just powersport web sites that the company who owns kawasakininja300.com actually owns.
285 websites, which will cost a minimum of $7125 per year to register with IANA (you didn't think domain names were free too, did you?), not to mention $14,250 per year if they have basic SSL certs on half of them (I'm not sure they have certs on any of them, honestly, but hey...). Not to mention web developers as each has their own identity, moderators (I'm assuming they pay at least some of the people moderating the forums), content creators if they're paying to create any original content...
You're making out like they get tons of money for doing absolutely nothing. The truth is that they do offer a service, one which you don't have to pay anything at all for, just give your eyes to advertising once in a while (and not even that if you use an ad blocker).