I have no idea why the Luftwaffe kept trying the multi engined connected engines. They didn't work well. They kept trying to use them in lieu of a 4 engine design.
Several factors come to mind:
Propaganda;
The entire Nazi machinery was build and thrived on propaganda - therefore speed/records was a main priority,
Fastest car, fastest motorbike, fastest train, fastest ship, fastest aircraft, etc. As such a 109 was ordered/favored instead of a He112. The same applied to bombers - they had to be as fast or even faster then contemporary fighters, as such speed was prioritized over bomb-load - therefore nonsense like the Do-17 and it's followup family, Bf110 and e.g. the He177 came in.
War planing and visions of war:
Adolf was aware that there was not much support within the German population for war - especially not for a long term war.
So everything incl. the industry was laid out for a short term war - simply over-rolling the enemy via mass and surprise. In order to keep the mass and surprise a secret - production-plants needed to be small and widely spread.
Aside from France there was no adequate adversary in Europe, and England due to being Germanic would logically side with Germany. The Soviet-union, just filled with dumb and incapable Slavic and Bolshevik folk.
The war tactic was entirely based onto attacking/destroying military targets, aka precision strikes - therefore this dive-bomber theme. Strategic bombing aka destruction of civilian and industrial targets - wasn't a topic and died of entirely with the death of General Wever in 1936. Therefore no viable production plants in regards to size and layout - that would have permitted the large production of sizable aircraft.
War production:
It was very important for the Nazi's to keep the population happy and content - aka the supply of commodities to the public and providing jobs was a priority.
Resulting in many but small sized factories - e.g. the aircraft industry. Nowhere near the dimensions of British Bomber-plants, or Soviet plants, and absolutely nowhere near the production/assembly experience and size of US plants. Larger aircraft such as the 177 or the Gigant, the final assembly partially took place outside the factory - or due to factory space limitations at an extreme slow pace within the plants.
No state run or controlled industry;
Adolf due to his concept/interpretation of "loyalty" never touched his initial sponsors - the industry.
As such no efforts were made towards centralizing production - a fusion of different company ownership's - not even a centralization of R&D capabilities and human resources - Every single war producer ran his own R&D e.g. the Horton brothers!! That "favors" and corruption ruled the relationship between industry and the state procurement departments - was known.
So taking all these factors together - and the reason for Notlösungen (Stopgap solutions) from 1943 onward becomes obvious. Not to mention the issue of obtaining raw materials to increase production and to keep a war in increasing scale going.
Just my 2 cents