Why would a jet engine use cannular combustors if the annular design is superior?
Single combustor cans are simpler to develop. To get the ignition and combustion process right in an annular combustor is quite a challenge. When the first jet engines were developed, Junkers decided for separate cans while BMW wanted to design a theoretically superior annular combustor. In the end, the troubles with the combustor meant that Junkers got their engine fielded much earlier, even though BMW had started their jet engine development before Junkers.

With today's CFD tools the annular design is not quite such a challenge any more.