Why Microsoft didn't kill the iPad with...

...the battery in Surface with the capacity just like in iPad?

It would give us +15 h of work and would kill all the competitors.

The reason was an additional price? Apple manage to keep it at reasonable level. Microsoft couldn't?

Or the engineering process? Battery to big? Apple manage to do that, why Microsoft couldn't?

Surface got medocire-resolution screen, so should provide much more battery life. Unfortunately it doesn't. Why Microsoft, why?