Then the sponsor either not generous enought, or does not know how to manage its investment properly.
The reason for saying they need a sponsor.
They are all heavily sponsored, even though it is "open source", without the big corps this "open source" won't really go too far.
The costs and investments generally aren't disclosed but it's not exactly free to create this operating system, as in someone sits and writes code of the goodness of their hearts.
There are sponsors, donators and so on.
Also, Linux is a mix of the kernel, the graphics environment and so on. It all comes from different sources.
Huge portion of software as well is written by big corps merely because they needed the software.
It is a similar situation with Android.
It is free and open source but if you look at how much Samsung and other phone makers have contributed towards the general codebase (not proprietary shells and bells), it is probably more than the Google contributions.
Microsoft is generally developers-friendly, Apple is very strict. You either do what Apple says or nothing at all.
For example, Apple kicked everyone out of the kernel long time ago, whilst Microsoft is still dwelling on that.
Without solid controls, it becomes very difficult for users to obtain quality software.
The requirement is just "it needs to compile and work".