Is this a function of Hollywood being filled to the cup rim with mediocre writers who never had to go through the discipline of weekly television scriptwriting or is it a function of lazy Hollywood writers convinced that they'll be bailed out by the effects?
No, it's a function of directors and producers having all the decision-making power and writers having none. Unlike in television, the feature industry treats writers as merely hired help whose job is to put the directors' or producers' ideas on paper. The standard writing process is an overcomplicated mess that usually involves a bunch of different people whose ideas are mixed and matched by other people.
Of course, writers can have power in features if they're actually doing the directing and producing themselves. This is actually to the Bad Robot people's advantage, because Abrams is directing and Lindelof, Kurtzman, and Orci are producing. They all came from television, and they're able to bring something more like the television writing process to the table and maintain more control over their work. Although they're still subject to studio pressure to conform to the big action-packed blockbuster paradigm. Another reason writers have so little control over big-budget movies is that there are just so many investors with huge financial stakes in the product that there's a lot of pressure to avoid taking risks and to adhere to familiar formulas. I don't think it's a coincidence that both STID and Man of Steel
had climaxes built around gratuitous massive urban destruction; studios just assume that's what audiences want to see now, in the wake of things like the Transformers
films and The Avengers
Plus, of course, there's the simple fact that a 2-hour movie doesn't allow you as much time to develop your characters and your world as you can in a weekly series, so the results are naturally going to be more superficial. Remember how the TNG movies made less effective use of the ensemble beyond Picard, Data, and Worf than the series did, and didn't really get to flesh out the ramifications of their events as the series could.