There are seven churches. Why do pre-tribbers think they can pick Philadelphia?

Thayers definition also has the word as guard which makes sense. Instead of keep thee from the hour of temptation it would be guard thee in the hour of temptation.

Also Philadelphia must overcome like the other churches.

Rev 3:10 Because thou hast kept the word of my patience, I also will keep thee from the hour of temptation, which shall come upon all the world, to try them that dwell upon the earth.

Rev 3:12 Him that overcometh will I make a pillar in the temple of my God, and he shall go no more out: and I will write upon him the name of my God, and the name of the city of my God, [which is] new Jerusalem, which cometh down out of heaven from my God: and [I will write upon him] my new name.