If you manage firewalls for people they can allow your IP to connect remotely while keeping it shut for everybody else coming in from the WAN, it's easier to VPN back to your own network with a static IP etc.
Static IPs have become more relevant in the past few years with the rise of altnets because often while you might not need a static IP, you don't want a CGNAT one, but lots of providers don't offer a public but not-static option because it would be a bit pointless, so people buy static IPs to get a 'real' one.