What’s the benefit of Band Steering when both bands work anyway?

I have a computer that can connect to a Technicolor DGA2232 router both via 2.4 and 5 GHz. As we all know, 2.4 is better for distance while 5 is better for speed.

But when the router’s band steering option is turned on (which is how it is by default) the computer only uses 2.4.

With band steering turned off, the computer can connect to the 5 Ghz WiFi. As soon as it does, the speed is very high.

So with band steering on, why does the router think it’s better to give this computer 2.4? Is it more stable? If so, how do you define “stable” in that context?