Because they fuck you over as a customer, they constantly try to push bullshit you don't want nor need on you when you buy stuff, and quite frankly, many of their employees are snobbish assholes. That has been my experience anyway.
I haven't shopped there since my Wii U pre-order almost 2 years ago. I had enough of their BS after that. Now, I'll go to Best Buy, Amazon, wherever. Just not there.