I also don't really understand why an open letter imploring people to play older games is needed, or what it's supposed to accomplish. Lots of people are already playing older games! So many older games have vibrant, thriving communities. It's probably a better time right now for retro gaming than ever. So it's not like older games are gathering dust and not being touched.I'm definitely in the camp of people who don't reject older games outright, but also don't embrace them automatically just on the basis of their oldness. In general, I know the kinds of things that I want a game to do, and so if a game does those things, I am interested, regardless of whether it is new or old. Hence, I love old-school D&D, Classic Traveller, Pendragon, and I also love PbtA games, Blades in the Dark and Fria Ligan's Year Zero games, but I have very little interest in actually playing any edition of GURPS, Vampire the Masquerade, Space: 1889, anything W.O.I.N. or Spire: the City Must Fall.
I suspect that, when push comes to shove, this is the case for most people. We all have a sort of mental framework for what we want games to do, and the age of the game by itself isn't really the determining factor. So a plea to play old games really only makes sense to a person who (1) has categorically rejected older games on an incorrect assumption that they don't do what the person wants a game to do and (2) actually has the bandwidth and interest to try additional games.
It's really lovely to go back and discover that an older game actually does the thing you want games to do after all, but it's sort of the product of a confluence of factors that's not always going to happen. So I feel like, at best, I can urge people to not rule out older games categorically.
EDIT: And I don't blame anyone for steering clear because of toxic scenes. I think that a lot of the toxic scenes are easily avoidable and have accessible non-toxic counterparts, but I also really don't blame someone for just not wanting to take the risk, especially when there is a lot at stake. There are like a million games out there and nobody has time to play them all anyway.
If the problem is that the people in your gaming circles don't want to play them, then it seems like the right move is to convince the specific people you want to play with to try the games you specifically want to play. Open letter's not going to do that.