Linux has a low footprint, similar to ARM, so the two were naturally combined for low footprint platforms like Android and Raspberry Pis.

The open-source ecosystem also helped. If proprietary software is compiled only for x86, then the best you can do, is to try to run them with a translation layer.
With open-source, you can compile them for ARM yourself. No guarantees that that will just work, but devs can contribute fixes and eventually the original software package can be officially released with an ARM package.