Well there's this thing called friendship. You see, executives at VC firms and such are typically pretty friendly with each other, and view their fellow executive's success as potentially pulling them up the ladder. AI is the next big thing. Sam Altman and his company is in a nice spot to profit. Moreover, YC research is an investor in OpenAI.

Thus, because the executives want Altman to succeed (to presumably advance their own career) and because they're in charge of YC, which is an investor in openai, they have every incentive in funding startups that then use OpenAI as the main platform.