Re: Because it can run a lot of software.
True, but also consider that many old apps and processes need access to the hardware that a VM can't provide for. Couple this with a manufacturer that cannot produce a proper Linux version because their management thinks it too costly or unnecessary, or a threat to their IP. Either way you slice it, you lock your systems down to some old rev of crap that will never, ever get updated. Now, you want to provide more products or services, but spend $0 money on the development, and security is an afterthought if not just; "don't put it on the net." That's why we can't have nice things.
I make my money moving shitty old apps to newer pastures. Or keep the old garbage barge from sinking. I don't care, the pay is the same. But I would never recommend to a customer that they should lock-in and never bother to update or upgrade, or move to open systems where this kind of crap has been dealt with already. You can slide an old OS into a VM template, providing there are no weird hardware dependencies. Migrate services and other apps to multiple VMs, or a big VM on a bigger machine. The problem then becomes the staleness of the OS and the need to migrate from older, EOL OSes to the new, and the ability or need to scale. Along with refreshing individual bits of the framework, without upsetting the apple cart. This is sure a lot more fun than chasing the Tuesday Patch Wagon.
This current shop I'm at is heavy into Windows and wrapping up things in expensive, support contractable, chunks of tech with excessive security, but they also have discovered the beauty and elegance and supportability of what you can do with a nice, low-cost, Linux farm. The proof is in the cost. The licensing on all the big-box apps starts to make less sense when you can build what you need out of open source wares. I see it at more and more shops now.