It's more for lightning. You don't want players getting struck by lightning. If it was just rain, they'd probably be going.....that said.....(I arrived on Friday) back during AC, they had an enormous queue for registration on the Thursday, and one of my friends got drenched in the rain during a storm.
And just our luck … imagine if any of these things happened.
Aubry kicks a game winning 70 yard FG in the rain … but wait …lightning strikes the ball just before it goes through the FG post. We lose.
DAK throws a 99 yard TD pass, but before CeeDee hauls it in…yep you guessed it … lightning strikes the ball.
Steelers like up for a game winning FG, it falls short…no, wait, lightning strikes the ball giving it a boost ..FG good, they win…
This is why they do not play in the lightning storm.