Generally because they prioritize ease of operations over helping customers overcome jetlag. In this particular situation I'd guess the ease of operation comes from:

* full customers are easier to deal with than hungry customers

* Doing meal service early avoids the risk that weather turns rough, making a late meal service hard/impossible.

* Crews are fresher earlier in the flight, and so are do a better job and prefer doing meals early.

* Waking customers up is extra work for crews, and may not be wanted by passengers.