Yeah, if you don't have your own hardware laying around it's definitely a bit of investment to get a server up and going if you want to do a witness as well. My guess would be that most people are using virtual machines in Amazon or Microsoft datacenters which is why we see such a high consolidation of our nodes in the top three countries. I haven't looked into it much yet but I'd imagine the requirements to just host a seed node aren't as intense as they are for a witness.

Cost is always a factor though.