I think they are overwhelmed by data on failures at the level of (low) quality FSD are now.
Having a team of 50 testers, seeking different cities, would be more than enough. Each of these days testing would net them a few hundred issues pr driver. When they don't report any failures for weeks, one can spread out testing further. But they are not there yet
Maybe the main reason for public beta is cost reduction, but I think that is the ancillary reason. Publicity, promises made, and keeping the innovation hungry fans satisfied is the main reason.
this seems unlikely. There's no reason Tesla would provide the ability to "overwhelm" themselves with snapshot button data to 60k testers if their main motivation was for publicity/promises made. I would be more inclined to agree if starting with the safety score cohort of testers, they didn't give us the ability to snapshot and kept that feature only with employees and the original early access cohort.