Browser support is necessary for a website to communicate with a hardware key (such as Yubikey). Yubikeys aren't automatic; you press a button to authenticate.
Maybe you don't like those, but they work well for many people. Even non-technical users are less likely to lose a key on their keychain than to lose or damage their phone. (I've lost Google Authenticator keys to phone hardware failure.) They can also be used by people who don't have a cell phone at all, or use it rarely.
They're also resistant to phishing attacks since they authenticate the site, and users are not good at checking domain names.
Maybe you don't like those, but they work well for many people. Even non-technical users are less likely to lose a key on their keychain than to lose or damage their phone. (I've lost Google Authenticator keys to phone hardware failure.) They can also be used by people who don't have a cell phone at all, or use it rarely.
They're also resistant to phishing attacks since they authenticate the site, and users are not good at checking domain names.