It's simple. As long as a significant portion of Apple's revenue comes from having a closed, "walled-garden" ecosystem, Apple will be disinclined to participate anything that might result in the demise of that ecosystem. After all, it's hard to be in the same boat as everyone else supporting WebAssembly etc., when that same technology will ultimately result in the death of on-platform app stores.
Apple's walled garden and iTunes revenue pales in comparison to their iPod revenue, which has been declining for 10 years straight. (It's roughly on order of a billion dollars). Just to compare, Macs account for several tens of billions of dollars. And iPhones/iPads account for hundred billion.
Apple's take from iTunes is small and not essential. Unlike Amazon whose business model IS to sell content, Apple's model is to provide content, to sell hardware.
Oh yeah, iTunes content sales include music and movies as well. (Apple does not break it out any finer grained than that).
Anything Apple does is to sell hardware - that's their main revenue generator. Everything else is just icing. Especially to encourage sales of new hardware.
Safari upgrades don't sell hardware.