Why did the later versions of AeroVodocody L-39 Albatross find much market success?
It was, although it's not in widespread use.

The L-39 was developed into the L-59 and from that into the L-159 Alca. It's radar-equipped, can carry just over 5,000lb (2,340 kg) of air-to-air and air-to-ground weapons, and is in service with the Czech Air Force. According to Wikipedia, 72 were built between 1997 and 2003.



Given that it's an aircraft designed in the former USSR's influence, it's not unsurprising that it didn't get a lot of customers. Russia prefers to buy Russian; Russia's friends also prefer to buy Russian. America's friends are strongly encouraged not to buy anything that isn't American. And thus a small Czech single-seater is not likely to become very popular.