Yes, cost, that knotty one. Forget cost for a moment, transfer port injection ( carefully timed and aimed ) will almost perform as well as DI at a fraction of the cost and complexity of DI. I'm only pulling your leg, all my bikes accept one has a carburettor but The EFI one is the most exciting and I think the way of the future. It offers a degree of engine control flexiblity that a carb never will.