How would Apple distinguish that from all the other perfectly good WiFi routers on the market?
Back when Apple's Airport stuff came out, it was certainly more user friendly, and more likely to work with Macs, than the PC-centric competition, but these days the competition has improved a lot and mostly "just works" with Macs and iDevices.
Many people already get a WiFi router bundled (or as a subsidised extra) with their broadband connection & these have the advantage of installation and support from your broadband provider, and many basic users will never need to look at the admin interface.
I suspect people who upgrade from their provided router will be looking for bells & whistles & complexity rather than Apple's trademark ease-of-use.
Not saying that Apple couldn't offer a useful product, but I don't see it getting much market share.