In fact one failed recently and my computer monitor was fried (so was our cable line and septic processor).I was thinking
To understand why it failed means learning how surges do damage and why that protector did not claim to protect from that type of surge. The concepts were originally introduced in elementary school science.
Lightning seeks earth ground. A path for a 20,000 amp electric surge is via a wooden church steeple destructively to earth. Wood is not a good conductor. So 20,000 amps creates a high voltage. 20,000 amps times a high voltage is high energy. Church steeple damaged.
Franklin installed a lightning rod. Now 20,000 amps are via a wire to an earthing electrode. High current creates near zero voltage. 20,000 amps times a near zero voltage is near zero energy. Nothing damaged.
Lightning seeks earth ground. A lightning strike to utility wires far down the street is a direct strike, incoming to every household appliance, destructively to earth. Appliances are not a good conductor. So lightning creates a high voltage. Lightning current times a high voltage is high energy. Appliances damaged.
For over 100 years, facilities that cannot have damage installed superior earthing connected low impedance (ie 'less than 10 feet') via one 'whole house' protector. Then high current creates near zero voltage. 20,000 amps times a near zero voltage is near zero energy. No appliance is damaged.
A lightning rod does not do protection. A connection to and the earth ground electrode defines that protection. A protector does not do protection. A connect to and the earth ground electrode defines that protection. Where was the earth ground connection for that failed protector? Does not exist.
Some incoming wires do not even need a protector. Best protection for cable TV is a short (ie 'less than 10 foot') hardwire connected to earth ground. No protector required. Telephone wires cannot connect directly to earth. So the next best thing, a 'whole house' protector (installed for free by the telco), makes that same connection to earth.
AC wires are entering without an earth ground connection if you did not install a 'whole house' protector. Even that monitor's protector and protectors recommended by others needs protection only provided by an earthed 'whole house' protector. A low impedance connection (ie 'less than 10 feet', no sharp wire bends, etc).
A lightning rod or protector are only as effective as its earth ground.