Why is Apple's Official Charger 20W when the New iPhone 16 is up to 45W?

I know very little about how charging actually works, but I heard the new iPhone 16 had a faster charge and could charge up to 45W. I was just wondering why the Apple Store allows you to bundle in their official 20W charger. Are all these 45W capabilities only through third-party chargers or something, or is it that the 20W charger is better overall for the longevity of the phone and is more practical from Apple's standpoint?