You are a security "researcher". Maybe that means you work with a group of bona-fide professionals, maybe that means you're still in high school.
Either way, you have the capability to break things. But, breaking things isn't trivial; you don't expect to spend a few minutes "poking around" and come up with something, especially something interesting.
So you have some choices. You can: try to break things which will give you rewards proportional to the time you spent and the severity of what you find; try to break things which will give you almost no official reward at all; or try to break things and then sell the solution to the highest bidder or make use of it yourself. (Let's assume that people aren't generally in the habit of working for free.)
Now then. You're Yahoo, with millions of user accounts and a not-great track record for security. What would you prefer for the hacker to do, and how would you incentivize them to do it?
You can gripe about "the community" or "entitlement" all you want -- until it becomes sufficiently annoying or unproductive -- but that won't change the end result, which is that companies which give substantial rewards for bug bounties are creating a marketplace where they win by getting lots of good talent to examine their systems without paying by the hour or day for it and the company gets first dibs on the details of the bug.
Companies which don't do this, lose.