Worth noting that Apple doesn't just cripple iOS Safari, it cripples all iOS browsers because it also forces them to use WebKit, the crippled browser engine underneath Safari.
It would be fine if they just made Safari bad, that's their choice. But they don't stop there: they make the entire web bad on iOS purposely to promote the native apps they can tax.
This is clearly for reasons of security.
I don't think Apple is terribly interested in market share for Safari. What they are interested is preserving their competitive advantage in privacy.
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Firefox was planning a native gecko based ios app. But Apple decided to limit it to EU forcing developers to choose to maintain seperate projects for a limited users.