Because, in 2026, hard drives are really small and can't hold much information, that we need to limit the world's freely and globally available editable encyclopedia, too what a select group of individuals consider noteworthy. No possible editorial bias there!
Hard drives can hold lots of data these days, and text compresses rather well.
You can write about whatever you like and put it on the web, just not in Wikipedia for which, as has been said exhaustively above, there are clearly laid out admissions criteria, not just the whims of a "select group". You are entirely free to contribute to articles-for-deletion process yourself.
Wikipedia does not exist to be a soapbox, self-publishing host or advertising medium, and having a Wikipedia article is not a human right.