If a big corporation wants to give you money,you will have to give something in return.
I don't believe that Coinbase wants to support Bitcoin Core developers only because of their faith in Bitcoin.
What if Coinbase provides financial support only to Bitcoin Core projects,which benefit the company in one way or another?
I know that consensus is need for approval of changes in the Bitcoin Core source code,but can a big wealthy corporation "bribe" more Bitcoin Core developers into approving a soft fork,which could potentially increase the control of Coinbase over the blockchain?This is just a hypothesis.I don't know the answers of those questions.
Doing "good deeds" can benefit companies. Plenty of companies are involved in charity for example, sometimes they get a tax write-off, but even then, it's a cost, it would be cheaper not to do it. They do it because it helps their image, it's good publicity, so indirectly, it's good for business.