Why do very few e-commerce websites use full-width and fluid layouts?

Looking at some of the top e-commerce websites (Flipkart, Etsy, Amazon, Bestbuy), I could find that only Amazon utilizes a full-width layout, and that too isn't fluid.

While I understand the demerits of full-width websites as far as reading and content consumption is concerned, why do most of these e-commerce websites have a cluttered and narrow layout?

My points in favor of fluid design:

• E-commerce platforms rely on rich imagery, and fluid layouts allow usage of bigger images.
• E-commerce websites have a ton of products to showcase, and full width will give them more room.
• E-commerce websites seldom have long lines of text and have space partitioned into sections.
• 960px is oh-so-old and most of the users have a 16:9 monitors now.
• Fluid designs provide a clean and immersive experience.
• Grid systems have become very strong and easy to use now, so fluid designs are no longer a pain to create.

Points against:

(Answers!)

Why I think the current scenario exists:

• Some of these websites came into existence when 960 was the norm, and they have grown too big and they are too lazy, lack innovation, or don't have enough resources to adapt to the new scheme (but they have huge manpower!)
• They are skeptical that it may drive orthodox users away? (but what about the next-gen user?)
• They feel that major change in the layout will cause loyal users to re-learn navigation from scratch (but we're talking about changing layout here, the functionality can remain same! And if google/fb have the guts to do redesigns, why don't they?)
• They want to play safe and stick with the tried and tested.

I've personally seen some modern e-commerce websites using clean and modern layouts (and copious amount of whitespace) and found them to be very appealing. ( can't recall their names right now)