Plenty of server-side FOSS is mainstream. Maintainability of the code is not the problem — there exist commercial support options. On desktop FOSS often has inferior usability for non-tech users due to different incentives for product development. If you ask anyone in the legal or accounting departments of a corporation, they will demand Microsoft (not even Google) not because it’s more expensive or has terms and conditions, but because they just can’t feel themselves productive when using alternatives. LibreOffice is not bad, but it isn’t great too.

> since the code may not be maintained and there may not be any support.

Isn't this an argument in favor of open source? Zoho may not be around forever, but open source code is, and you could just pay someone to work on it.

Try getting support from google

Open-source has many technical advantages over closed-source, in addition to the moral ones (which are quite powerful themselves).

Being able to inspect the software you use makes you able to trust house it works, and fix it at points where it's not working; those were the first motivators for creating the FLOSS movement.

There's also the advantage that in the long term you don't depend on the company developing the software; if the company goes under, or simply stops supporting the software, you can hire a different batch of developers to carry on maintaining it. That's the reason why many big contracts require that the software vendor puts the source code under escrow.

In reality, closing the source of software only benefits the seller; everybody else benefits from having it available. With FLOSS, you get that for free.