"there needs to be enough beekeepers that are buying insurance out there to spread the risk around"
That's not the case. The ones bearing the risk (insurance companies or reinsurers) need to diversify their risks overall but they don't need to do this within risk types.
If you put aside the scale economies of doing the calculations, an insurer would have less overall risk (by which I mean variability in outcomes) if they were to insure one beekeeper, one driver, one baker etc.
No need to have a large beekeeper market from a risk perspective. Maybe from an underwriting efficiency perspective, though.