Very simply put, the weather may not be in your area. Planes are either
3. on Scheduled or unscheduled maintenance.
They don’t take breaks, and they don’t have parking lots where extra planes just hang out. If a plane isn’t flying, it is losing money.
So the plane for your flight has to come from somewhere. If that flight is delayed due to weather, your flight will be too. They can’t just bring a plane around from the back. So other flights out of your airport have birds coming from other places with better weather. Their flights won’t be affected.
TL:DR; weather delays don’t always refer to weather in your area.