That assumes all of the spammers care enough to learn the limitations of txt.fyi.

Some will just scribble whatever, where-ever possible.

I can confirm that. I made https://pastery.net, a pastebin (THE BEST ONE), and I looked a few weeks later to find that it had a few hundred thousand pastes. I was very happy to see that people were using it that much, until I realized that most of it was spam.

I wrote some heuristics to delete spam pastes, and only about 1,000 pastes were left, about half of which were spam still :(

I don't even know why they do this. They just do it.

Require some complex js codes workflow to post using websocket or something and most automated spam goes away. They are mass mindless bot, not targeted spammers.

That's a good idea, but most of the functionality of the site comes from its API. Then again, it's easy to require a key and a captcha to sign up, so your idea is good, thank you.

Cheaper for their scripts to indiscriminately spam than them manually work out which forms and public sites are indexed and will actually bring them value.

YOu just gave them a lab to play test in.

it happened to something similar i did many moons ago , even with nofollow. i dont know why

Nofollow links seem to help with getting the target indexed. So, the spammers create their second and third tiers of actual content on sites that do not use nofollow. However, they'll use anything with any kind of links to get those tiers crawled and indexed.

i guess thats what they did. funny, it seems they got penalized regardless somehow, because i started getting emails asking to please remove the spam they posted.

Edit: It seems some of them were trying to damage competitor's SEO ranking by posting irregular links. SEO is wild west.

Thankfully the old "blasting links" type of SEO is pretty much dead now.

When you say something similar do you mean also not indexed, or do you mean you ran a text submission site with nofollow links?

nofollow, but indexed

I'm not convinced that nofollow == no value.