Being just a platform didn't work so well for Atari (see the crash of 1983). And both the Apple and Play stores have a terrible reputation for allowing (nearly) anything on their stores, which is something that Nintendo would want to avoid.
On a PC, you get the freedom to install what you want.
On consoles, you get a certification of quality, integration, and style for the console. Everything fits with well-defined hardware as well. And since it's just video games, it's not a huge deal if it's limited, you can always install indie games on your actual PC.
With an app store, you just get shovelware that is unduly promoted combined with a gatekeeping what software you can run on your device, which could have otherwise been open.
