This isn't just personal sites. Large blogs (Gawker), whole news sites (Vice), and other content no longer exist, because cynical corporate parasites bought them out. Newspapers that exist from before the internet era are arguably better archived on microfilm, Google Books etc, than today's news. The Internet Archive and other sites exist, but they are nonprofit and can't keep up with the sheer scale of content being pulled down.
Also strongly disagree with your assertion that some sites don't need to be saved. The whole point of archiving is that we often can't judge what is important to future generations