Because the swathes of people that are invariably wearing the latest cash shop item are literal walking advertisements for it. By disabling glamours you're likely never going to see these outfits unless you actively keep an eye on the launcher ads for them. In this regard it's not too dissimilar to why advertisers don't like you running ad-blockers. The average person who wants to run a blocker is going to be ignoring the advertising on these pages, yet even so, every now and again you'll get a bite from something that's actually of interest.
I worked for EA (via Bullfrog at least) at one stage, does it show? =(