A lot of those 90s games had straightforward goals that were easy to understand. Sure, they could be hard, but that's different from being complicated. Games like Tetris or Street Fighter II had simple rules that led to deep play. The frustration was part of the charm, not a barrier to fun.
Honestly, I read something once about how old arcade games were designed to be easy to pick up. They had clear rules that anyone could get in seconds, but getting good took time. That's why they're remembered as fun, not just frustrating.