Just because SEO spammers posting hidden text doesn't mean it's going to work. It's done pointlessly because it doesn't work.
I disagree. If it doesn't work at all or bring any benefit, there would be far less SEO spam and i wouldn't bother create this thread.
But after March 1, 2020, Google treats links on NOFOLLOW sites as a hint to index or rank a site
rel="nofollow": The nofollow attribute is for cases where you want to link to a page but don’t want to imply any type of endorsement, including passing along ranking credit to another page, Google said.
Today vs March 2020: Today Google will treat the nofollow attribute as a hint for ranking purposes. Meaning Google might count a link as credit, consider it as part of spam analysis, or for other ranking purposes.
On March 2, 2020, Google will use it also for crawling and indexing. That means will Google use it as a “hint” as to what should be indexed or crawled...
So SEO spam is now being used to try to index or crawl a site, especially a new site.
There are other ways for your website indexed by Google though[1-2], so i have doubt their goal is having their website/url indexed though. Although it's different case if Google refuse to index their website by human request.
[1]
https://search.google.com/search-console/about[2]
https://developers.google.com/search/docs/crawling-indexing/sitemaps/build-sitemap