In the US, the majority of adults are invested in the markets (https://news.gallup.com/poll/266807/percentage-americans-own...), whereas in Europe the number of people invested has historically been lower (https://www.ft.com/content/31c4d453-498e-4cc2-b14f-d7e8b17b9...).
This makes sense when you think about it - in the past you would have built habits and understanding from relatives and your community (e.g. "Don't invest in stocks that's gambling and they always crash!"), whereas since the Internet came along people have more access to data and perspectives from more places.
All of the above said, the last few years, and especially since the lockdowns, the behaviour in the markets has been really alarming. The FT.com link above touches on this, but the rush into [stocks/cryptocurrencies/leveraged funds/options] is something I've never seen before in my lifetime. I don't think the world has ever seen anything like this level of amplified speculation. Bitcoin, Leveraged ETFs, and Options didn't exist in the 1920's. The Netherlands had futures contracts towards the end of Tulipmania, but I haven't seen anything to say that they were leveraged.
In the late 1990's it was clear and readily apparent to everyone that the Internet was a massively important step forward. We agreed on that. It wasn't a controversial or widely disputed viewpoint. The market still imploded because of the sheer amount of rampant speculation, so to think something worse won't happen to a multi-trillion dollar market based on a technology many people think only has value for running Ponzi schemes seems to be pretty irrational.
To top it off, the wall of hype seems impenetrable at this stage ("have fun staying poor!" etc), so it remains to be seen what happens when the plates stop spinning this time.
tldr; Your grandparents might be proven right after all.