Because it IS the best option. Temperature checks are theatre, and don't matter when it only takes one asymptomatic, maskless person to spread a deadly respiratory illness.
Are you reacting to somewhere that was doing temperature checks, but not requiring masks? Relying on temperature checks alone is clearly foolish.
In my experience, I've only ever seen temperature checks at doctor's offices and hospitals, where they also have mask policies so "thorough" that I sometimes have to argue to keep my P100 non-glasses-fogging respirator on.
In my experience, I've only ever seen temperature checks at doctor's offices and hospitals, where they also have mask policies so "thorough" that I sometimes have to argue to keep my P100 non-glasses-fogging respirator on.