I probably have done more serious research on GFCI protection than anyone I've met. I've read at length how it works and why. it protects folks from shock by interupting the flow of electricity before it reaches a a danger zone. old 120 volt breaker protection would protect you, but your gonna get a jolt. 240 breakers can cause damage or death before they trip. GFCI's do not protect the home. they are not designed to do that. your breakers in the panel do that. breakers trip because of shorts, overloading, heated lines, or fire.
GFCI's trip because of an imbalance between the neutral and the line loads. this is caused by resistance because of moisture or when someone touches one or both of the bare wires of a system. The degree of imbalance between the neutral and line loads before the button pops is extremely variable based on the individual plug itself. although the human body can't even feel a 12-14 volt AC "leak" because of a wet cord, the GFCI detects it and usually trips. older GFCI's that have tripped multiple times, thus have weaker springs tend to trip with a 3 volt imablance or less. newer 20 amp plugs will trip less and can usually withstand more moisture and can handle 6-8 volt imbalance or so.
If you read any article on the internet out there, it talks about tripping gfci's and how many efforts to reduce it are useless. taping plugs can help until the water gets past the tape. then it won't dry out. elevating plugs off the ground helps until the rain makes a continuous run to the ground.