My kitchen faucet water pressure (hot only) is very very low. What can that be.

It can be debris in hot water side of the cartridge, clogged supply line and/or clogged angle stop. I would first Close and then Open hot water angle stop under the sink to see if it helps. If not, then close water, remove water supply line and flush clean under running water in another sink. Take faucet apart, remove cartridge and clean passages. Reinstall all. Remove Aerator. Turn water back on. Run w/o Aerator for few seconds. Reinstall Aerator.

Let me know how you did...