It may just be that my perception is biased due to the algorithmic nature of YouTube recommendations, but it does appear as if a lot of 5E players have become more interested in the OSR as of late.
Again, I know it may just be that having watched one video about turning from 5E to the OSR, the algorithm is recommending more similar content to me. But all of the videos that have been recommended are fairly recent. Most have been made within the past few months, and none more than a year old.
So, why is this happening?
Well, for one, it may just be a YouTuber fad. One streamer or vlogger tries out an OSR game, and others feel curious to try it as well. People see one person's idea, and they will copy it. Expect more of these videos to be produced if this is true, but don't expect a huge increase in new OSR converts.
Another possibility is that 5E fatigue has set in. There's a reason WotC recently announced their "One D&D" revision/new edition/whatever it will be. People have explored the possibilities of 5E, and one more splat book of new options is not gonna hold their attention much longer. Part of this is baked into the design of 5E, which like 3E and 4E, was designed as a game of system mechanics exploration more than imaginary exploration within the game world. That gives it a limited (intentionally so?) lifespan with the players.
Final possibility? It's not a trend at all. There are a handful of people who have done this, and YT is just showing me all of the small number of videos like this. In a week, I won't be seeing any more because I'll have sampled all there is to sample.
For the sake of argument, let's assume that there is actually a trend.
Not every one of the videos I've watched has been positive towards the OSR games they've tried, but the majority have been. And these videos have spanned the gammut from playing the actual old editions from TSR to all the various retroclones (well, OSRIC, LL, OSE, S&W anyway), and OSR adjacent games like Black Hack and Dungeon World.
Despite the bad reputation of THAC0, or Vancian casting, or high lethality, the fact that most of the older editions and their retro-clones encourage exploration of the game space more than exploration of the system mechanics is, I think, the reason why people are engaging with these rules again. That's what happened with me and a lot of other people 15 years or so ago.
And then there are the folks that have been playing the old editions all along, and still are having fun with them. And new folks are joining these games, and finding out that you don't need a bunch of fiddly numbers on your character sheet, or kewl nu powrz! at ever level to have fun.
I'm not gonna make a prediction that One D&D will flop. I'm sure there are vastly more people willing to take whatever WotC will give them. And it looks like WotC is gonna try for more of a subscription model rather than a purchase model of sales, at least for their online tools, this time. So they'll probably secure a decent revenue stream with their new version of the game.
But I will say that the OSR is far from dead. I'd expect a lot of these 5E converts to be coming up with their own retro clones and modifications to the game and releasing them in the next few years! Even if it is just a handful of people splitting off from the 5E community (or straddling both), there's new blood in the OSR. And they will run (and create) games that attract even more people.