I don't have enough choice over who provides my electricity. I don't have enough choice over who provides my cellular service. I don't have enough choice over who provides my Internet service. I don't have enough choice over who provides my television broadcasts. But app stores are a much higher priority, evidently.
Utilities like electricity are often (at least in the U.S.) in their own category i.e., natural monopolies. They are regulated more strictly by state and/or local governments including what services they are required to provide, pricing requirements, etc. I am pretty sure Apple/iOS and Google/Android would not want to fall under that added level of regulation.
Apple/iOS (with around 67% share) and Google/Android (with around 33% share) are dominant players in mobile OS in Japan. That combined with their alleged anticompetitive activities are I assume (don't know Japanese law) why they are facing antitrust complaints.