It's not the screen size, it's the demographic shift. By 2000, only half of U.S. households had a shared living room PC, mostly for work and/or games. Everybody having a phone in their pocket later was a change that we did very much have to account for. Non-technical people can be scammed very easily into life-ruining mistakes with a little social engineering and a little bit of access to powerful tools already on their devices.

I remember when big sites started having to put big banners in your browser console warning you that if you weren't a dev and someone told you to paste something there, you had been scammed, and not to do it. They had to do that because the average Facebook user could be tricked very easily by promises of free FarmVille items or the opportunity to hack someone else's account, and those are fairly low stakes bait. Now people bank with real money on their phones.