Why would they incur the cost of retrofitting their factories or production process for a small minority that wants removable batteries. If there was enough demand they'd know because they'd market it as a feature and profit from it. Truth is normies don't care or prefer the look/feel of soldered batteries and unibody slim phones. I'd personally like all phones to have an unlocked bootloader but I know that's not what the market wants and manufacturers rarely offer it. I can't force them to make one for me so I just ignore them and buy the one with an unlocked bootloader.