A tripped thermal switch
Some fireplaces have a safety switch that kills the main burner if the unit gets too hot inside. It’s paranoid, but it’s protecting your house. If your fireplace ran for a while recently, let it cool down completely—like, two hours—then try again.
You might hear a tiny click as it resets. That’s the sound of relief.
The remote or wall switch is dead
This one makes me laugh every time. You’ve been troubleshooting for an hour, swearing at the pilot light, and the issue is a $1.50 battery in the remote. Check the batteries. Check the wires to the wall switch.
Fireplaces are fancy, but they’re still just appliances. Sometimes they need fresh AA’s.