Current job is focused on $x and I want to do $y. I guess that's similar enough to new challenge/learning?
Another reason - job is too easy and undemanding or there just isn't that much to do. I could have coasted and collected a paycheck (I did for a little bit) but I just knew that it's bad for me to stay there long term. I imagine this is some people's dream job though.
And more money of course is a factor. I once left a job that I really enjoyed doing for one that I suspected wouldn't be that great just because I could more than double my salary (it's not that impressive, I was just severely underpaid at the first job).
Another reason - job is too easy and undemanding or there just isn't that much to do. I could have coasted and collected a paycheck (I did for a little bit) but I just knew that it's bad for me to stay there long term. I imagine this is some people's dream job though.
And more money of course is a factor. I once left a job that I really enjoyed doing for one that I suspected wouldn't be that great just because I could more than double my salary (it's not that impressive, I was just severely underpaid at the first job).