why didn't they open the door

I've never really thought about that. I think it depends where about in the house the baddies were, I can't really remember but if they were on the higher floors there was a chance they could hear the door opening. There were a few things that bothered me about this film. If your daughter is so ill then why not have a insulin kit in the panic room, I know they had only moved in that day but I would have thought it would be an important thing to do.

I thought it was odd the panic room had fireblankets but no ventalation or air purification system. Or oxygen mask. Or even a gas mask!

The bad guys were all in the master bedroom which contained the panic room. Had they opened the door, they would have had nowhere to go. The wall which Forest Whitaker smashes to expose the pipes is the same wall with the panic room door on it, as you can see the broken mirror which Jared Leto had previously broken in frustration when they had first escaped him and been able to lock themselves in the panic room.

Because the bad guys were right at the door. They'd have been instantly caught.