Dozens of reasons for this, including many brick and mortar stores switching to self checkout, keeping a pitiful selection in store (WalMart:don't see your size/color/preference? Order online from us! Customer: Why bother, I'll just add it to my Amazon order and not have to drive to the store at all), sorry excuses for customer service (I want to find a bluetooth hack and blast bestial war metal in all the cashiers with earbuds in everywhere).
While taking away from the big box stores doesn't bother me, I know this tread is hurting the mom and pop storefronts much worse.