Why ? The concept is sound and - at that time - proven. Only the Porsche engines were crap.
Eases up a damn awfull lot of drivetrain, steering and gearbox problems. ... With the pay-off of bigger overall-weight compared to a working driving-stearing-gearbox-system-solution.
I don't think that the diesel/gasoline-electric powerplant for the ground vehicles is that much of a benefit unles there are batteries involved, so the regenerative braking can be used to improve the mileage. There is also no way of using both electric and fuel engines for greater acceleration, since the power deployed to the tracks will be smaller than what fuel engine can provide.
Even if we use one engine, that means one generator and either two smaller on one big electric motor. A too big a draw on German limited copper production if we're planing to produce the new tank by thousands; Germany is already using aluminium radiators for aricraft, rather than the ones made from copper.
The 'normal' mechanical transmision was not a boogaboo in 1930s/40s, especially if the weight of the AFV is kept under control.
Unfortunatly I have (atm) no idea of the state of art on diesel-engines at that time in germany.
Jumo is producing diesels for aircraft (Napier has a license for Jumo diesels for the UK pre-war), MB is producing them for many users, with many different cylinder numbers in a V. Designing & production of a V-12, say 30 liter diesel is no rocket science.
Can use the turbo well, as the Jumo diesels did, since the exhaust gasses are not as hot as with gasoline engine.