I'm someone who watches a lot of old anime (around 190/410 shows, movies, OVAs, I've seen are from before 2000) and I think that's the case, but a big part of it lies in the settings and genres.

You have way less shows from say 1991 set in school with a 14 year old protagonist, whose goal in the story is to get a girlfriend despite him being a computer nerd gamer who has no friends or personality for example.

This kind of bullshit did exist, but rarely was it the focus of the narrative. The seasonal format popularized around 2007 encourages a lot more shovelware Anime desperate for sales, so both safe profit plots you've seen a dozen times before as well as horny-bait have become more prominent.

Another factor are the artstyles. The 80s and 90s tended to have more realistic artstyles , where you could more easily distinguish the characters' ages. Of course, more cartoonist artstyles existed, such as in Rumiko Takahashi's work or the later Slayers/Pokémon style, but moe or so called lolis really only took off after 2000, being either rare (the former) or mostly confined to highly questionable VHS-only content during the mid 80s (the latter)