Those are not businesses. They are free projects which a dedicated person (or group of people) donate their time and energy to produce.
Wikipedia has their semi-annual donation drives and many (not most, but enough worth mentioning) FOSS devs are salaried by companies like Google and Microsoft and are allowed to work on patches to out-of-scope projects on company time provided they're still fulfilling their main roles. There are also Liberapay, Open Collective, Ko-fi and such but for the majority of FOSS devs not funded by large corps, just developing a large and widely-used program because they want to, donations rarely ever cover as much as they would make at a 9-5. There are also nonprofits that distribute donations to FOSS devs. For most it is a money pit, but to them the passion is worth more. They do it for the love, not the money.