A lot of them are either companies that were once customers but unsubscribed, or just one off individuals from those companies that tried it once, but never deployed it to a larger group.
Not just SaaS stuff. Displaying logos to imply endorsement is a common thing across the board. It's purely a marketing move, and as with all marketing moves, you can't trust any of it.
i felt like the only ppl that believe those things are managers that read gartner reports
Unfortunately those are the same people in charge of buying decisions in big companies…