Confession with true sorrow and regret is necessary for forgiveness but we are also taught that accepting that we sin and asking for forgiveness is not good enough. We must avoid sin. If you have premarital sex or use contraception in your marriage, then asking for forgiveness isn’t good enough if you repeatedly do it knowing it is wrong.
The avoidance of sin is ONE of the things Catholics believe. Some bible thumping protestants live for forgiveness, and sing about their sins rather than behaving better and avoiding sins and doing the right thing in the first place.
Should married Catholics all just be rabbits, abstain, or leave the church?
True contrition is necessary, but lots of people repeatedly fall into sin. If they can't resist temptation, they need to pray for the grace to resist.
Of course it's hard (virtue is hard) but the fruits of contraception have proved to be promiscuity, divorce, pornography, and abortion. Even C.S. Lewis called that one, a long time ago (you will find the quote in The Abolition of Man, I believe). So you trade a passing convenience (not having to do the hard work of NFP) for horrific societal and moral consequences.
It's the same for all the other innovations you propose. They have already played out in the Episcopal Church, and the results are horrific. They wouldn't be any different in the Catholic Church. Isn't the definition of insanity repeating the same actions while expecting different results?