Many of the first, second, third century Christians also read documents such as the Didache and the Shepherd of Hermas and other non-canonical works sullied by either false stories or Pharisaical traditions of men, just like today many JWs read the "Organized to Do God's Will" book or "Shepherd the Flock of God" book and consider it to have equal weight to God's Word. Jesus said to beware the leaven of the scribes and Pharisees, and we are wise to continue following that counsel today.
Jesus did a lot of things during the days since his resurrection.
The context of 1 Peter 3:18-20...
"For Christ died once for all time for sins, a righteous person for unrighteous ones, in order to lead you to God. He was put to death in the flesh but made alive in the spirit. And in this state he went and preached to the spirits in prison, who had formerly been disobedient when God was patiently waiting in Noah’s day, while the ark was being constructed, in which a few people, that is, eight souls, were carried safely through the water."
Jesus was obedient to God to the point of death. Jesus could have misused his authority, misused his power the same way the the disobedient angels did by taking advantage of the flesh of others for selfish gratification, but Jesus didn't do that. Jesus was obedient. Noah was also obedient. Noah built the ark, doing the work God assigned him. He was figuratively "resurrected" to new life by means of going to figurative "death" in the ark and then coming out of the water again at God's appointed time. When Jesus "preached to the spirits in prison" after his death and resurrection, it was Jesus' faithful example to death that proved those disobedient angels could have maintained their integrity under their much easier circumstances during their assignments back before Noah's time. The angels who were assigned to take care of humans didn't have to abuse their authority and sexually assault those in their care. They didn't have to go on power trips and demand to be worshipped. Jesus maintained his integrity under more tempting and difficult circumstances. Those wicked angels had no excuse for what they did. Jesus' faithfulness to death sealed the deal for the judgment on those wicked angels, and their condemnation is irrefutable.
The context of 1 Peter 3:19 as well as 2 Peter 2:4 and Jude 6 makes clear that Peter and Jude were emphasizing we need to be obedient to God and that the adverse judgment on the incorrigibly wicked is deserved.
Soon Jesus will execute judgment on those in the religious institutions who follow the lead of the wicked angels by misusing their authority in order to abuse the sheep in their care and get worship for themselves instead of God. Jude said it...
"Too bad for them, for they have followed the path of Cain and have rushed into the erroneous course of Baʹlaam for reward, and they have perished in the rebellious talk of Korʹah! These are the rocks hidden below water at your love feasts while they feast with you, shepherds who feed themselves without fear; waterless clouds carried here and there by the wind; fruitless trees in late autumn, having died twice and having been uprooted; wild waves of the sea that cast up the foam of their own shame; stars with no set course, for which the blackest darkness stands reserved forever."