Wrong.
Pope St. Pontian, in 235, one of the first bishops of Rome, who was arrested and sent to the salt mines, and in order for a successor to be able to be elected in Rome, he resigned his office.
Pope Benedict IX, in the 1040s, resigned and attempted to re-acquire the papacy several times.
Pope Celestine V resigned after a shor time in the See, and Gregory XIII resigned as well.
You are claiming no popes were ever imprisoned or martyred, and they were cowards? You are ignorant and should stop spreading anti-Catholic lies.