I am by no means an expert but just going by logic, you can imagine that most planes are designed so that a stiff wind or weather wouldn’t knock them out of the sky. Flights aren’t being delayed/canceled because they’re busy cleaning up all the wreckage.
The delay comes from other reasons. all of the smaller personal/charter flights that actually would be unsafe have to be reorganized or diverted. If a plane has to divert or circle the field a couple times that causes delays. With airports it’s all about knock-on effects. Once one plane is late, the delays will pile up eventually leading to cancellations. Also, remember that the flying conditions at 30k feet are different from ground conditions. So a plane may easily fly above the weather but be delayed from actually landing due to ground conditions. Keep in mind, the last thing an airport wants to do is start delays or cancellations because of just those knock-on effects. Imagine the shitshow it would be if 100% of flights out of an airport were cancelled. Literally millions of dollars are lost every hour the airport is shut down.