What do you mean by modern? My understanding is that the rise of index funds has been the biggest trend in this space over the past 20-30 years. Riskier bets like individual stock picking, or "experts" that con others with dubious ways of predicting the future, have been around forever.
* All stock market stuff feels modern, because 15-year-olds don't talk about it but 25-year-olds do. So it feels like something that wasn't really around/popular when you were young.
* Some would say retailer investors who want to buy individual stocks should be holding them for the long term - and that a mobile app, letting you trade on the go, is an anti-feature.
* The rise of Reddit's Wall Street Bets, who glorify moves that seem really dumb.
* The rise of Cryptocurrencies, and/or their marketing to unsophisticated investors. If I put my entire life's savings into Dogecoin, does that mark me as someone so dumb you should save me from myself?
Apps like robinhood encourage and even gamify frequent trading at the expense of naive investors and because that's where brokers make money. Coinbase and their ilk do the same in the crypto market. Frequently trading stocks, and doing anything in crypto is just as much gambling as betting on a sports game, appeals to the same demographic, and is just as destructive.
Yes, stock picking and penny stock scams have been around forever, but it has never been so easy.
Coinbase exposes an api that lets you do some pretty interesting and powerful strategies. Let's see a bank do that. No, seriously, I'd sign up tomorrow for a bank like that.
Mobile apps have made it easier for people to do sensible strategies like dollar cost averaging. Fractional shares, recurring buys, and no fees were not something easily accessible to your average retail investor before mobile apps began introducing these features.