Because unlike the phones you mentioned, the glass formula has been changed. The glass is actually harder to shatter, but the tradeoff to that is it's easier to scratch.
This became really obvious on iPhone 11 and there is a thread about iPhone 11 which is a mile long. If your iPhone 11 Pro Max didn't scratch, you're extremely lucky. (Simply do a search here for the iPhone 11 thread about scratches and you'll see how many were just as upset about that phone). People simply didn't or don't understand the physics of glass makes it impossible to make glass which is equally hard to scratch and break. The new Corning formulas Apple is using this yeas, called Ceramic Shield is 4 times less likely to shatter if dropped. But it's not difficult to scratch.
You can shoot the messenger if you want to be mad at me, but I've been trying to explain this to people who seem to not understand your phone doesn't have the same glass previous phone.
Read this article about why the iPhone 11 scratched so easily --> Why is my iPhone 11 getting scratches?
The ONLY way to ensure your phone doesn't get scratches (if scratches annoy you, like they annoy me) is to put a good quality screen protector on it. Otherwise, if you get scratches, Apple isn't going to do anything for you. They consider this cosmetic damage and that's not covered under your warranty. And this is also why Apple installs screen protectors on phones in their store. The Belkin Screen Protector is an excellent choice and what has been in my last few phones.