Probably it's the same person/web agency casinos go to ? Or all the sponsors are entities from a larger casino/betting group and the inside dev./web agency uses bulma et voilà.

Looking at the links: probably not. These look like shady casinos and casino affiliates. Most likely they do it for cheap high quality backlinks. Several of them promote unregulated casinos targetting the Swedish market.

Cheap SEO backlinks

$100/m is cheap for a back link? (honest question - I've no idea).

67 logos on the home page at the time of writing this, that's $6'700/m. While obviously not FAANG salary scale, it isn't to be sneezed at either.

There are/were places where you could get really cheap (or free!) backlinks, but most search engines got wise to that trick, and those backlinks (links from spammy sites with little organic traffic) aren't very valuable anymore. To get a link on a reputable standalone website, $100/m seems cheap to me. What better alternatives are there at this quality level? A B2B partnership/sponsorship? You can easily spend 5 digits for that.

> $100/m is cheap for a back link? (honest question - I've no idea).

Depending on the backlink and ambitions for the website in question, I personally don't see that as unreasonable.

They have a lot of money to launder. Better to spend some of it to reduce exposure, and increase SEO ranking.

Personally I'm not political about that but it's unfortunate Bulma chose to hide them now.

They’re still showing for me

SEO, probably a cheap way to get a link from a high PR website.