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.

Who said anything about billions? I just said that it costs money to pay people to work on OSS, which is accurate as ImGui is sponsored by companies and Qt is a commercial entity with infamous licensing. VC doesn't necessarily mean billions in funding.