There might also be some sample bias. "These deaths" are people who started their manga/anime/videogame/etc. careers in the 1980's-1990's when they were in their 20's-30's on average. People are starting to get old. Yes dying in your 60's is young but as pointed out, given the workaholic culture it's not that surprising and for every person dying that young there are still hundreds others living, they just don't make the news.