[ausbah]

my guess is simple because 99% of people have their needs met by the app store and / or have no interest in side loading because it's too technical for too little benefit

[vorpalhex]

It's 30 seconds to sideload an app on Android.

Many good apps are available by sideload only. They seem to do well enough.

[salawat]

...The too technical part being self-inflicted by the requirement for yearly hundred bux and a working mastery of cryptography utils.

[j-bos]

This applies to android as well