The capital costs associated with entering the phone market are obscene but many companies have tried, some have succeeded in other countries but in North America most have failed. I don't really buy the argument that alternative app stores will make any significant difference to consumer habits but some people think it would. People have also argued for the break up of Apple or Google but so far no one has a made compelling legal case for it. Most of the arguments surrounding this are about developers rather than consumers which is part of the problem, no one has been able to demonstrate any significant harm to consumers. Despite the often pilloried "walled garden" used by Apple and Google, consumers have huge variety of choice of literally millions of apps, free and paid. We have easy access to phones of various sizes and prices, though market forces have shifted toward larger phones in recent years. It's a consumer's market right now and for the foreseeable future. If that changes one day then it will be easier to argue for say forcing Apple to break out the App store into a different business entity or something similar.