Obsolete tech will be replaced but many teams will not use the latest version of the software, simply to avoid running into bugs and issues introduced with new versions. Besides that, there is no point looking back.
Absolutely, lots of devs still use old versions of UE including UDK. It can be useful to troubleshoot or isolate problems or measure performance… Plus if you’re a student or just starting out and trying to learn, but are priced out of the market for GPU’s, or live in a country with unfriendly import taxes here’s an option. But should you start ‘new production projects’ in UE4 or UE5? Here’s some hints about that: