I'm not saying they're bad designers, in fact they're excellent - they're fulfilling their brief perfectly by bringing to market the required product at the desired price point.
What I'm getting at is Lego have changed from trying to be the best at what they do to making the most money as possible. As part of this they are "buying in" designs from IP's and bypassing the R&D and subsequent brief creation elements associated with creating a theme from scratch. Without this the licensed sets are just the best model you can make to fit in with the desired price point - therefore the brief is determined by money people and not creative people.
When given enough headroom in the price they come up with some great sets but more often than not, it's all about the figs with a token build - eg microfighters, battlepacks & sets like 75169, 75200, 75205 from this year.