Surely the plan for the war was to quickly conquer and occupy enemy territory while still valuable as the German economy would not survive a lengthy war?Germany always wanted to have strategic bombers like the cool kids, their problem was that their aircraft industry was nascent due to the ban on military aircraft production in Germany and thus the need to start it up from scratch in the 30's (barring a few clumsy attempts at trial building bombers as "mail planes" in Swedish factories). Since 4 engine aircraft are pretty complex Germany wasn't up to the task and it was simply easier to produce single and double engine aircraft, both of which worked well for ground support missions. That being said, it was always envisioned that the He-111 and the Ju-88 in particular would be "dual purpose" bombers, able to perform both ground support and strategic bombings. When the Ju-88 failed to evolve into an aircraft capable of larger bomb loads this idea fell through. The problem was that the actual strategic bomber, the He-177, was repeatedly delayed from deployment due to technical issues. Having been ordered in 1936 and having its first flight in 1939 it was deployed first in 1942, way too late to serve in its intended role or having much of an impact on anything.
It is not that the Luftwaffe didn't want to be able to lay waste to entire cities like the Combined Bomber Offensive did, it is that they didn't manage to get the necessary aircraft to do so until it was too late.
Also, I had read that one of the limitations on 4 engine aircraft was simply a limitation of the number of engines they could build, and 2 engines bombers obviously require less.