You're right; a slight one, possibly. But the margin of error on the forehead scanners is so high you're not going to detect anything other than the most serious of fevers, which I guarantee people can tell they have.
If you want proper temperature checking you're going to have to get into oral checks, which nobody is willing to do. The forehead scanners are a placebo -- this has been known for a very long time: https://www.reuters.com/article/us-thermometers/accuracy-of-...
The real reason though is people tend to think it ain't that bad and go out. Fever checks stop those people before they infect your shop.