Here on Linguistics stackexchange (not meta), we have very few users and even few interested ones, also the votes and replies to good questions are fewer than most of the other communities, also the questions die very frequently without an answer, having smaller bounties can be encouraging :)
I think, this question at Meta.SE and its answer(s) sums it up very well:
If you did this, there would be no point of having bounties - because every user would start a bounty on their questions.
(I think, this thread from comments worth added into the answer)
The main concern of those who may want to see smaller sized bounties is that bounty can be "expensive" for a low-rep user. However, the expensiveness is always relative.
For instance, I noticed that on [travel.se], each my post receives more votes (see, I'm not an active user there, yet having 2k rep) . Hence, it is easier to earn reputation points, hence a user is easier to expend 50p for bounties.
So, in my opinion, we should struggle for more voting per post, rather than for lowering bounty limits.