Current LiPoly replacement batteries are
not sold as consumer items. You can't buy them off a peg at a normal retail store. Take a look at phone batteries sometime and make note of the logos everyone ignores.
A UR mark (its a backwards printed UR) is a UL certification for components meant to go in a UL listed product but themselves aren't individually certified as UL products. Not that UL or any other testing labs are the end-all be-all of safety but in liability terms they are important.
The UR testing means the component isn't outright defective for purpose when installed in the UL listed device. So if there's ever a lawsuit around a device and all the components are UR labeled and the product is UL listed the manufacturer is unlikely to be forced to recall that entire class of device.
In order for a battery to get UL listed instead of UR listed it needs additional testing (money) and any sub-models or major changes need to be retested. It's much easier to get UR labeling for a component that can only be used in the intended UL listed device. Phone retailers do not want component-only certified things sitting in warehouses in shitty retail packaging.
Besides the whole liability issue there's issue of scale. Manufacturing a hundred million widgets with glue to hold batteries in place is more efficient than screws. Screws require screw holes, assembly is slower, and screws work themselves loose with thermal expansion/contraction. Glue is more efficient for assembly and overall safer over the life of the device (measured in the total manufacturing run divided by defects from battery slippage).
Devices could require fewer disassembly steps but it would be at the cost of assembly complexity. A $1 more in assembly costs is an extra hundred million it costs Apple or Samsung for just one model of phone.
I know Apple is just evil and can do no right but there are reasons shit is built they way it is. iPhones are far sturdier and resilient than they were ten years ago and their batteries last as long/longer despite higher power draw of their SoC and radios. Part of that sturdiness is gluing pieces together to better handle impacts and batteries that have more power storage per volume because they do t need thick impact shells. There's pretty good odds that making an iPhone with less glue and more easily replaced batteries would lead to more phones going in the trash due to them breaking more easily.