They are kind of mutually exclusive, for several reasons.

First. a non-removable battery allows for more flexibility as to the shape of the battery, which allows you to cram more battery into a laptop as you can more optimally use the space you have.

But a bigger reason is that lithium batteries are dangerous, if punctured or otherwise damaged they can catch fire in a quite spectacular way. This means that if you have a removable battery it needs to be inside some kind of protective casing. This takes up space, so you end up with a smaller capacity battery for the same space.

Also, batteries do not degrade that quickly anymore, and they aren’t that expensive to replace either.