Two things: the range offered for instore pickup is far larger than the range held in stock. You don't have to pay delivery costs either. If something is the same price on Amazon as in Tesco [my local supermarket] then I'll order at Tesco and not pay delivery as I know I'll be there in the next few days.
Sometimes I'll "click and collect" just to be sure that the item is in stock. For example I did a price comparison recently to buy a bike saddle, it was cheaper (including postage) from Halfords and I can add stopping there to my journey for very close to zero cost (except time). If I'd ordered it from Amazon then I'd probably be out and end up having to travel to my local postal distribution office, less convenient and more expensive.
Sometimes I'll "click and collect" just to be sure that the item is in stock. For example I did a price comparison recently to buy a bike saddle, it was cheaper (including postage) from Halfords and I can add stopping there to my journey for very close to zero cost (except time). If I'd ordered it from Amazon then I'd probably be out and end up having to travel to my local postal distribution office, less convenient and more expensive.