I'm not sure that the shift towards less interactive board games is generational, because I'm not really sure the generation of board gamers changed.

What I see is gamers who were playing high-conflict games such as Twilight Imperium in 2005, were then playing low-conflict, moderate-interaction eurogames in 2015 (such as Terra Mystica and Imperial Settlers), and then the more or less the same people are playing low-interaction eurogames today. It might be not only the case of changing generations, but also case of changing tastes within generation.

The reason for this might be that the adults are often less competitive than teens, and it's often harder to play aggressively against your spouses and kids, so when people get those, they also tend to switch to less conflict-heavy games.
 

I don't play board games but I'm very aware of what a huge growth area its been commercially these last few years. We barely used to sell them at all and now we have a whole room full of them and they're all over the rest of the shop, too.

I suspect the nature of board-gaming has changed enormously to include many people who would never have played in the past and also to become a much more social experience. In the context of "board game nights" where families and friends come together primarily to socialize with games as a kind of peg to hang the get-together on, it makes sense that co-operative games or at least non-competitive games would be more appropriate. Whether that's a generational shift or just a more general, social drift is another matter.
 

Also, since Scrabble is literally the only board game I do play, I feel I ought to point out that it was originally conceived as a co-operative game, in which players try to achieve the highest collective score, and that it can still be played that way if preferred. No need for a new game, just a tweak to the rules.
 

Another reasons is that game designer have become more competent : part of the appeal of a game is solving puzzle, and a human opponent is far more likely to provide a complex situation to solve than a fixed set of rules.
If you look at the history of card/board games, you see game designer learning how to design game with interesting challenging puzzle, that stay interesting game after games.
When you combine that with Baghpuss comment, maybe it is simply that game designer are more and more capable to create game that target a new market.

At least in France,in the 90s, the non agressive part of the games were very shallow.
 

I play board games, but the last few years since I play more with family, I/we have trended more towards cooperative games. There little fun to be had in dunking on the more casual players, both for the casual players and for the more victory-minded. Cooperative allows a nice mix without excluding anyone from the games.

I am not sure kids learn about competition from board games, they seem to be steeped in that learning curve way before stepping into adult board games. I do think competitive board games should exist, and they are great depending on the people. Cooperative games just serve better in a different environment.