Why do cascaded compessors have a type instead of just a size for fixed width columns

When compressing data knowing the type can be helpful interms of determining the best compression plan to utilize but when you have a plan that you want to execute why does it care the type of data that is being compressed?

Having to specify the type prevents users from doing things like

std::shared_ptr<Compressor> compressor = nullptr;
plan_details.type_size = whatever size we want to set here
if(use_lz4){
   compressor = std::make_shared<LZ4Compressor>(plan_details);
}else{
   compressor = std::make_shared<CascadedCompressor>(plan_details);
}