There was the type of complexity that had the player do more. This was the old kind, more skills, more button presses, more weapons, etc. The player had more choice and had to work more to accomplish something.
The second type of complexity, the one that almost universally game developers love more and more, is that an action the player does has more effect in the game world. The metaphor that might work best is throwing out a single stone, but having more ripples.
Now, it's easy to see why game developers might like the second one. From their perspective it's cooler to build. They get to do more, and see more results from their work. And the player get's to see more results from their actions. It seems like a win all around!
But, this is a thing I just thought of, and I've seen zero game developers realize despite my somewhat obsessive hobby of seeing what they're thinking about. If you reduce the first type of complexity there's less for the player to do. There's no two ways about, giving the player less options, means there's less gameplay for him or her. There's less game to, your game. Oh sure, you could argue that players might have to think more about their actions, since they have somewhat larger ramifications. The player has more to watch now.
But playing a game isn't about watching. It's about action, that's what separates them from every other form of media. The consumer is an active participant, and this notion of "less to do more" is actually "less for the player to do, with more results." Giving the player less to do is, well it's just less. Advancements in games are supposed to give more for the player to do. Giving them more to watch, more to react to is all well and good. That's perfectly fine fun. But there's no reason that anyone must simultaneously give the player less actions they can do.
Edit- As for the reduction in skills specifically, I would love to have seen more gameplay mechanics added than a reduction in choice. Adding a quick way to dodge and/or the ability to cling to and shimmy along edges (neither overly difficult) to acrobatics would have been a funner thing to do than eliminating it (I'm assuming it's been merged with athletics). Similarly having mercantile get you better quest rewards and/or having it affect how you bribe people to say, not arrest you for a crime, or even not report a crime, would have been funner than merging it with speech (again, assuming here). That way people would have had more game mechanics and just as much choice. Rather than less choice in exchange for being more likely to use those game mechanics. After all, a big part of TES has always been "choice" and eliminating some of that doesn't seem like the best idea.