I think 'death' is kind of an overdramatic way to put it :'D A skill plateau is not the end of your creative career; if you actually are good enough to consistently draw in an audience (as demonstrated by the existence of actual readers in actual reality you can point to, ofc
), I see nothing wrong with just resting on your laurels if your goal is to just reach people rather than 'being the best creator you could be' ¯\_(ツ)_/¯ (And besides, you can always change your mind and resume your learning whenever you want :P)
I wouldn't say this is the biggest cause, but I do see people that set too quick of an output pace for themselves for updating their comic, and they seem to just not improve very much over time. I suspect this is because they're not giving themselves enough breathing room to lean and try new things; they have to settle for 'good enough' in order to meet their schedule.
Maybe this applies for writing as well? My sample size for novels is considerably smaller because I tend to not read many, and also because it takes way longer to judge writing skills than art skills :'D But the logic seems generalizable, at least XD