Compared to a carburettor, fuel injection has many more parts that 'may' fail, a carburettor is a simple thing that works fine most of the time, carb ice can be a problem, that's why the pilot is furnished with a carb heat control and is supposed to be trained in its' function and operation.
The GA industry is not flush with cash, and updating an Aero engine is not the same as Toyota or Mazda bringing out a 'new and improved' model, it is a very time and money intensive operation to 'prove' a new design is reliable and fit for purpose, that's why aero engines look like they come from the 30's and 40's , because it is so hard to change an approved design.