Suzuki, how can you make an engine so bad?!

Why does a 970 cc suzuki SJ410 use almost as much fuel as a 1930s 3-litre citroen?

Comparison between the 1978 F10A suzuki engine (present in the SJ410/jimny) and 1938 15CV citroen engine (present on the 15CV traction avant)

First of all, i want to point out that i know the purposes of these cars are different, but my main problem is not the performance, but the fuel efficiency, which is quite absurd.

I own both a suzuki sj410 from 1984 and a citroen traction 15CV familiale from 1954 (engine introduced in 1938) and i write mostly from my experience, i sent photos of the cars and their engines above.

Suzuki SJ410 Citroen 15CV familiale

Engine size: 970 cc 2867 cc

Nr. of cylinders: 4 cyl 6 cyl

Horse power: 45hp 77hp

Curb weight: 850kg 1440kg

Max. speed: 110km/h 130-140km/h

Engine year: 1978 1938

FUEL CONSUMPTION (my own estimates) :

Suzuki: ~11L/100km

Citroen: ~12-13L/100km

Why was suzuki, after creating a cheap car, incapable of developing an economical engine?