Will an entity choose to pool their data in a collective?

It comes down to if they could even plausibly go it alone and come out first, second, or third.

If not, they'll join in.

If there's even a little bit of a chance of coming out on top, they'd give more to the collective than they'd get and thus won't participate.

If their contributions would dwarf the contributions of everyone else (or even would be the far and away majority contributor), they won't participate.