The data isn't available because PaleMoon doesn't collect any analytic or telemetry data. So they don't know how big their userbase is. (Recently though, I think they have started collecting some data on hardware because they wanted to revamp their code base. See this discussion - https://forum.palemoon.org/viewtopic.php?f=5&t=30909 - I however don't know how extensive, or persistent, this data collection is / was).