The brits had to produce CS and 2pdr versions of their tanks because they used single type units with incompatible specs. There was no way a slow Matilda could operate with a fast Crusader. And the CS versions ended up being mostly used for smoke laying. The Germans used mixed Pz III and IV units, since the tanks had similar enough specs. They had two tanks because they came from rival companies. The two countries that had a rational "one type at a time" policy either had a centralized economy (USSR) or built a tank industry from scratch (USA) Both France (H-35 and R-35) and Britain (Matilda and Valentine) had two types of infantry tank.
If you think of aircraft, the USA, with a developed peace time aircraft industry, also had competing designs from different companies.
If you think of aircraft, the USA, with a developed peace time aircraft industry, also had competing designs from different companies.