Conspiracy theory: Part of Apple’s goal with Liquid Glass is to make PWAs look further out of place.
While you can somewhat recreate the glass effect on the web, it is difficult, likely less performant, and isn’t 1:1. This will enforce a stronger separation between native apps and web apps.
Icons also presumably won’t be dynamic and adaptive to Liquid Glass’ styling, like they aren’t with iOS 18’s light/dark/tinted variants. This’ll make them stick out and feel more different than they already do, as well as look bad on the home screen.