Why won't my shower's temperature handle let the water get hot enough?
Many faucets have an adjustable range.  In the last one I installed there was plastic ring with v-grooves around the outside of it: to adjust the range you positioned two stops that hooked into the v-grooves.

Recommend the TIA* approach to see what you can see - it may be very straightforward.  Just don't drop the screws down the drain!

*Take It Apart