The reason IT jobs are down is a combination of things:
1)Too many people went into it, because it was seen as hot yet didn't require a degree, just certs (or nothing).
2)Improved knowledge of computers by the general public, and improved software for them to use (its not like the 90s when you had to really know Windows to set up a network). Not many people need to call helpdesk to plug in a mouse anymore.
3)Automation and improved infrastructure. It takes fewer people to manage a fleet of machines because the software is better.
4)We don't fix hardware anymore. We replace it. This is a lot lower effort. Also a lot of the hardware is more reliable.
IT jobs went away because demand decreased while supply increased. There's still a fuckton of jobs writing software, but we don't need as many people to take care of the hardware and administrate the systems. Those jobs aren't going completely away, but they'll never spike again.