As an anesthesiologist, I can guarantee you that anesthesia is WAY more stressful and intellectually rigorous than pain is. Yes, there are lazy stupid people in each profession, but anesthesia is way harder.
People see the anesthesiologist reading or playing a simple game and think they're just zoning out, when in reality they're listening to everything going on in the room and preparing plan A, B, C, and D for every little eventuality that might kill their patient. We work hard to make sure they never happen and everybody just assumes that anesthesia is easy when nothing happens. And trust me, there are LOTS of things that damage patients.
Anesthesia is currently so hot right now because a confluence of factors. One, we got hosed hard during covid and many people simply retired early or quit. Also, it seems that there is an ever-expanding number of locations that need anesthesia staffing and new surgeries that need anesthesia as well.
Meanwhile pain is getting relatively hosed, but it's still much better than standard PMR/Neurology/etc. Now that anesthesiologists aren't applying, there's some wiggle room for the non-anesthesia folks.