Making the battery removable would compromise on other parts of the design. Personally, a replaceable battery is very low on my list of wants.
[0] https://www.ifixit.com/Store/Mac/MacBook-Pro-15-Inch-Retina-...
Laptops should have replaceable batteries. Period. If you get a new laptop every 2 years and don't know what it's like to have a perfectly good MacBook with 30minutes of battery life, then maybe you can just imagine being in that position and consider how globally impactful this anti consumer practice is.
What the heck, all MacBook batteries are replaceable! Apple will do it for you in the first 6 years or so, and after that there are still 3rd party shops who will happily replace it.