if it's voluntary and companies will make more money by not doing it, then at least some are not going to do it.
So, from my point of view, this effort is mostly meaningless. It's not enough to get me to open my websites again, anyway.
Would it?
The primary purpose of robots.txt is not actually to lock out bots (that's why respecting it is not mandatory). It's to give the bots guidance as to which parts of your site are appropriate for them and which parts are not.
This may make the "clear intent" argument weak in court.
The standard has the keyword "Disallow", not "Avoid". I can't speak for anyone else of course, but that seems a pretty clear indicator of intent to me. By that I mean a site's stakeholders want to indicate that certain bots are disallowed from crawling a portion of their website.
I'm not saying a court wouldn't find intent signaled, I don't know, only that it's not clear-cut that it would.
What isn't known is if those sites will still have their content possibly included in training corpuses from CommonCrawl or ThePile, etc.
What isn't known is if those same sites will be also included in corpuses such as CommonCrawl or ThePile, leading to being included in training as is.