Like everyone else said, funding=/=ownership. I do suspect, however, that part of why these big tech companies fund Linux is because they rely on something built on Linux in one way or another. Linux tends to be the better options for things like servers, low processing devices, and more, and if they keep funding it, it continues to exist so they can use it. You'd be surprised about how much of the world actually uses Linux in some way.
Like everyone else said, funding=/=ownership. I do suspect, however, that part of why these big tech companies fund Linux is because they rely on something built on Linux in one way or another. Linux tends to be the better options for things like servers, low processing devices, and more, and if they keep funding it, it continues to exist so they can use it. You'd be surprised about how much of the world actually uses Linux in some way.