Because it's the least-likely position to be staffed by a company. It's the "least important" person to have.... until it breaks. Often a company relies on routing-switching engineers to do DNS instead of hiring a dedicated DDI engineer (DNS, DHCP, IPAM). It saves money in the short term, but when shit hits the fan... no one knows how to fix it because DNS is really easy until it's not. DNS is super simple at a basic level. But it goes way deeper than most people realize.

Because its always DNS

Because DNS is the user-facing part of the whole system. There is plenty of trouble with everything else, but you usually don't see that as a user. Also it's a hierarchical system with big providers/governments giving and taking names as they see fit, so there is always the possibility to get screwed.