Swab tests don't provide immediate results... though testing is starting to become available with results in 15-45 minutes. But still not practical -- Swab someone, then have them stand off to the side for 15-45 minutes??
But temp checks are more than a fake measure just to promote safe feelings.
Don't confuse elimination of disease transmission with reduction of disease transmission.
Yes, asymptomatic people *CAN* spread the disease. But symptomatic people are more likely to spread the disease. And coronavirus does produce symptoms in 50-75% of those infected.
So imagine -- No temperature checks, 50 infected people walk through the gates. Of which about 30 are symptomatic, and the most highly transmitting.
With temperature checks -- Only 20 infect people get through the gates, and they are relatively low transmitters.
Which scenario is better? 30 high transmitters + 20 low transmitters, or just 20 low transmitters?
Temperature checks are certainly not a guarantee... but they do make things safer. Extra handwashing stations are not a guarantee, but they make things safer. etc, etc.