You have to remember that a lot of those thing are either 1.0 holdouts, have been replaced by a better system, or both.
Battle leves were phased out because beast tribes and daily hunts filled the "daily exp activities" without also competing against crafting for resources. They didn't "forget" about leves, they intentionally replaced it with a more efficient system.
Guildhests are basically just combat mechanic tutorials. Sure they could keep adding more, but to what end? Unless they drastically up the exp/tomes, which they probably won't on account of them being to short and easy, why would anyone bother running them more than once?
Same with Grand Companies. IIRC, the last time the devs were asked about it in a Q&A the answer was something along the lines of "since GCs don't really do anything, there's no point in adding more ranks until we decide how to proceed with them in the future."
As for things like Eureka and Bozja, personally I'm okay with content having a shelf life. Not everything needs to stay relevant forever. I don't know about you, but I was already tired of Bozja long before ShB ended and was more than happy to let it go and move on to something new. It'll still be there if I ever feel like grinding out another relic.
