Or they could just use a permissively licensed OS, like one of the BSDs. There's no need to use a proprietary OS in order to avoid the GPL, pretty much all the

Or they could just use a permissively licensed OS, like one of the BSDs. There's no need to use a proprietary OS in order to avoid the GPL, pretty much all the BSDs shun the use of GPL code and they offer similar abilities to Linux. Generally, but have no direct knowledge of John Deere's situation, Linux is used because it's usually possible to have drivers which are already written for the various hardware which is desired in more embedded systems. Having to write or port something like a wi-fi driver to a different OS is very non-trivial but wi-fi is generally considered table-stakes now for lots of devices. So it saves significant cost and development time to choose Linux simply because you can get off the shelf drivers for your electrical design.