It baffles me that people need an explanation, but I'm happy to lecture educate on this subject anytime.
It's simple.
Websites cost money and time to host. Your typical static pages site doesn't take much, but a server with enough resources to run a highly demanding dynamic forum such as TBT can easily climb into the hundreds.
I also believe people deserve to be compensated for their efforts too regarding of the form. It takes a lot of time, effort, and costs... whether you're writing and editing content on a blog, producing videos on YouTube, or even running a forum.
So I ask, if ads are placed in reasonable locations in a reasonable quantity (so the page isn't COVERED in them, I don't support that either) and the website is providing a service you consider valuable, is the inconvenience to you really so bad that you insist of blocking them still? Will you really be that inconvenienced by say, a 90 pixel tall leaderboard above your content? Probably not. It's a great way to support people without putting front any of your own actual money. There's zero cost to you, yet you can still support costs and compensate creators.
This isn't about TBT at all either. I recommend that everyone turn off adblock by default on all websites, and manually block websites with bad practices. Because don't get me wrong, there are plenty of sites out there with very unreasonable ad placements, which is usually the reason that drives people to block ads in the first place. But many sites are not like that, and it's unfair to punish everyone.
Disclaimer: I do operate a couple websites with Google Adsense on them that I generate profit from. If you think that makes me biased, that's okay, but I think it makes me more qualified to speak on the subject since I know what it's like to have your ads blocked.