New games are just .. different.
I don't think it's that they're more complex, if anything having more buttons makes many simpler, as you have buttons associated with various actions rather than having to rely on multiple keypresses, or everything being context sensitive due to a lack of buttons. Also similar games tend to have similar mappings, things are more standardized than ever, pick up some old PC (or 8-bit computer games) and it's pretty much pot luck as to what the keys are.
The older games, I think were actually more mentally challenging, pixel perfect jumps were part about timing, and part about knowing and being able to measure things right down to the alignment of your character with a pixel, it was almost a puzzle.
Modern games are all gloss, you don't have that level of control, or knowledge but as a result they tend to be more forgiving.
Modern games also spend half the game holding your hand through them, older games do none of that.
So while all the action might be very 'in your face' and full of distractions they're not really harder, or more complex in any way at all.
I think the main difference is that pretty much every game today is just a story, you're expected to save progress, they're not just 'pick up and play for 10 minute' type games where the gameplay is usually based around a simple but novel concept, although there are plenty of 'casual games' which fill that gap too. Actually I'd go as far as saying the whole 'Casual' games term is a bit of a misnomer, because quite often it's in the smaller titles you find the real gameplay and the real mental challenges, not just something you can brute force your way through if you play it often enough.
I was never a big fan of books & movies growing up, I preferred the more abstract and challenging mature of games, it therefore doesn't surprise me at all that these modern games, which basically ARE movies, where you simply act out little bits to hold the story together have waned my interest in games