There used to be no AFK timer but it was implemented a couple of years ago if I remember correctly. Then it was much shorter, 5 minutes I think, and after the community complained about how short it was they extended it to what it it now, which I think is 15 minutes.
Yes, it’s about server resources. EHG has issues with them clearly.
The lack of persistent instances and the AFK timer showcase that fairly well.
So maybe in the future, when they get their network code under control far enough so they can afford it. As well as other optimizations which improve the situation overall.