speaking specifically of melanomas though, of the ones that are on cutaneous skin the majority appear to be related to acute sun damage - ie mayos who live their lives mostly indoor going out to the beach or wherever and getting fried (there are a subset related to chronic sun damage, though they have a somewhat different profile). and even a few instances of sunburn under the age of 18 is particularly correlated with melanoma later in life. yes some/many damaged cells may die off (either by triggered apoptosis or just necrosis from all the damage), but a lot will accumulate damage that doesnt trigger responses. but the problem is not just uv causing dna damage that triggers proliferative pathways but that it also causes dna damage that knocks out the cell death mechanisms when the damage is great enough to trigger the kill switch, and it doesnt have to be in many cells. if youve fucked up your skin enough that its sunburnt, youve done some bad damage that cell death and the inflammatory cleanup response wont fix