According to the National Center for Educational Statistics, about 8% of teachers left public school teaching last year, about the same as 10 years ago. Private school teachers leaving was 12%. Some people leave the profession before retirement, but a lot simply retire.
https://nces.ed.gov/whatsnew/press_releases/12_13_2023.asp
I've worked in the field for roughly half a century, and the same complaints made 50 years ago are made today. Amped up a bit to be sure, but as Will Rogers once said (in the 1930's), "The schools ain't what they used to be, and they probably never was."
I have a PhD student researching teacher attrition right now, and the #1 reason for leaving the profession (other than retirement) in her data was "school climate" followed by "work-related health issues" and "burnout."
It takes a ton of dedication to be a really good teacher, and it can be hard to keep that dedication up. It's not all that easy to even be a mediocre to poor teacher, but there are a number of folks at any given time who really should be shown the door. But if you want to improve schools, you have to make them positive places for both students and teachers. There are plenty of examples of such schools, but it isn't an easy proposition and it takes constant attention.
I went to school a long long time ago, but when I was in school, teachers were almost never absent, and most were really good. A large part of that reason, that often goes ignored, was that in the 50's and 60's, doors were not open very wide for really talented women to become anything other than teachers. Teaching had the corner on the market of smart, dedicated women. The women's movement changed all that (and absolutely for the beneift of society), but it came at a cost for education.