They literally said this is the reason in their marketing.

> features an entirely new material called Liquid Glass. It combines the optical qualities of glass with a fluidity only Apple can achieve

https://www.apple.com/ca/newsroom/2025/06/apple-introduces-a...

But yeah, it is a pretty clever way to make most cross-platform toolkits stand out and create a desire to create true native apps which increases their moat and means that some apps will have only an Apple version (or a worse app on other platforms) rather than releasing the same app on all platforms.