So recently I was made aware of the Asus Zenfone 3 Zoom. Here's a terse comparison of this phone to two of the currently top tier phones: (the reason I chose Plus and XL versions was due to the fact that their dimensions are comparable to those of Zenfone)

Asus Zenfone 3 Zoom [0]

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Battery: 5000mAh

Dimensions: 6.07 x 3.03 x 0.31 in

Weight: 170 grams

Screen: 5.5"

Price: $329.99 [3]

Apple iPhone 7 Plus [1]

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Battery: 2900 mAh

Dimensions: 6.23 x 3.07 x 0.29 in

Weight: 188 grams

Screen: 5.5"

Price: $969.99 [5]

Google Pixel XL [2]

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Battery: 3450 mAh

Dimensions: 6.0 x 2.9 x 0.2 ~ 0.3 in

Weight: 168 grams

Screen: 5.5"

Price: $849 [4]

So through this overview, the phones are relatively the same size, weight, screen size, and yet the top tier smartphones' battery capacity is greatly behind that of the Zenfone. Why is this the case? I understand that the three phones may vary in camera, processor, build quality etc hence justifying the price difference a bit. But I have trouble understanding as to why do the top tier phones not focus on increasing the battery capacity, which clearly can be done as demonstrated by Asus. I would gladly be willing to compromise on some of the Pixel/iPhone parts/features for a greater battery capacity.

[0] https://www.asus.com/us/Phone/ZenFone-3-Zoom-ZE553KL/Tech-Specs/

[1] http://www.gsmarena.com/compare.php3?idPhone1=8064&idPhone2=8065

[2] https://madeby.google.com/phone/specs/

[3] http://www.bestbuy.com/site/asus-zenfone-3-zoom-4g-lte-with-32gb-memory-cell-phone-unlocked-navy-black/5833504.p?skuId=5833504

[4] http://www.bestbuy.com/site/google-pixel-xl-4g-lte-with-32gb-memory-cell-phone-very-silver-verizon/5656048.p?skuId=5656048

[5] http://www.bestbuy.com/site/apple-iphone-7-plus-128gb-black-verizon/5581629.p?skuId=5581629

EDIT: Fixed spacing