As a developer, a huge reason I don’t mind walled gardens is the massive reduction in piracy. I’m glad people want to download & pirate the apps I poured blood, sweat, and tears into... but I’m not down with theft. Each dollar I earn represents the time I’ve spent away from friends & family.
I’ve worked on games that have been copied outright. All assets and artwork, but a new name and “publisher” being sold elsewhere. It eats into profits.
When the walls come down, developers will be knocked off. This will hurt indys far more than larger companies, as “developers” opportunistically exploit the work of others.
Apple & Google are great at reducing and shutting down this kind of activity. If people can install the Pirate Bay store and install anything for free, many folks will.
If users can be coaxed into privileging an app, malware will control the majority of phones. People are still falling for the Nigerian prince scam.