Click on the “search” tab and you will see that all of those WAN2 sessions are https. Most of the web is HTTPS today. This is because your HTTPS rule is before the default rule. They are not cumulative, they are “first to match”.
You have selected “auto” rather than custom. Use custom and set the ratio to zero for WAN2. Or put another HTTPS priority WAN#1 only rule above the HTTPS rule and allow “fall through to next rule” if it fails. (this would only be needed with multiple backup WANs. )