Why don't we have the chance to put a bounty on a question on meta? There may be cases where a person's question does not get due attention just like it can happen on the main site?
One problem is that there are no reputation points on meta, thus it is not clear which points should be used "to pay" the bounty, and even more where the answerer should gain them. (For the first one might say, just use the points from main, but for the latter this is not really a good idea, to give points on main, for meta content.)
Furthermore, the volume on meta is not as high. Thus it is not as likely that things fall through the cracks.
Yet note that on the network-wide Meta Stack Exchange, which is a site in its own right, there are reputation points and thus also bounties.
In brief, I think for per-site metas the idea is not really feasible without major changes, and it feels not so needed either.
Thus, I am against this feature.