GPUI development predates Sequoia's funding by about two years.

Companies start with founders funding themselves through savings and friends and family rounds before institutional investors are usually even interested. But make no mistake, they start it as a commercial venture, otherwise they wouldn't have taken VC in the first place, nevermind that VCs wouldn't have funded it if not for their pitch on how it could become a billion dollar company.

And since Sequoia? It is primarily the Zed team working full time on it, which costs money.