Because everybody runs Linux for last like 20 years. Data centers, network appliances, storage appliances, smaller devices of all kinds. It's in the open, the mindshare is colossal, expertise working with kernel and writing drivers is relatively easy to come by.
Everybody runs Linux because it's free, there is no danger of closed private forks gaining any traction, there is no danger of it playing MongoDB. So everyone can safely pick it and invest into it. The pace of progress is very high because of that, and anything broken would be fixed very-very soon.
Because of that ability to rely on Linux being a common thing that nobody can privatize, huge companies like Red Hat and Canonical could form, and entities like IBM, Oracle, Intel, Google, etc could keep investing in the development.
All the above is sort of problematic with FreeBSD. It's too cathedral on one side, and has too few strings attached to hold to it on the other side. So it remains the choice of connoisseurs who need its particular technical brilliance (e.g. the network stack) or its very permissive license (see PlayStation).
> Grsecurity fully complies with the license of the Linux kernel, the GPLv2. Since grsecurity is delivered as a source code patch, it is not possible under the terms of the GPL to offer a free version under an actual restriction that it be used only for evaluation purposes. Any customer receiving a grsecurity patch receives all the GPL-granted rights and responsibilities, including the right to redistribute patches in their possession or even to sell them to others.
Forks are completely fine. A lot of hardware, often not even esoteric, is supported by non-mainline kernel versions.
Everybody runs Linux because it's free, there is no danger of closed private forks gaining any traction, there is no danger of it playing MongoDB. So everyone can safely pick it and invest into it. The pace of progress is very high because of that, and anything broken would be fixed very-very soon.
Because of that ability to rely on Linux being a common thing that nobody can privatize, huge companies like Red Hat and Canonical could form, and entities like IBM, Oracle, Intel, Google, etc could keep investing in the development.
All the above is sort of problematic with FreeBSD. It's too cathedral on one side, and has too few strings attached to hold to it on the other side. So it remains the choice of connoisseurs who need its particular technical brilliance (e.g. the network stack) or its very permissive license (see PlayStation).