https://mathstodon.xyz/@tao/117237320796901560
Especially in recent years the mathematics community has worked very much in good faith, and a lot of effort is spent trying to give appropriate credit for ideas. Even when ideas are discovered in parallel if it turns out that previous work contained the same essential idea it is by and far regarded as best practice to give priority in this case. The point, in good academic practice, is to maintain the health of the practice at large.
As Terence Tao explains in that post, the goal of mathematics is not only to solve big problems. And, even if one were very single-mindedly focused on solving big problems, it is still (in the long term) better to maintain the health of the community at large so that problems which are out of reach at the moment may be in reach again in the future. Good academic practice is one part of this culture.