First things first, I have pretty average memory, I don't forget important things too often, but I also can't instantly memorize things to the tiniest details like some gifted people can.
Around 5 years ago I decided to memorize my wallet seeds to have one extra backup method. My main backups are pieces of paper + a flash drive with wallet files.
I am just amazed after reading about your experience, more likely confused too. Because you need no to remember them, there are plenty of ways to keep your phrase safe and disconnected from the digital world. But you still tried to memorize it and from so long years. No wonder, if someone keeps repeating the same phrase for over 5 years he will definitely memorize it. But as i said, it's an unnecessary task.
Well, if you really want to safe your key phrases safe for a longer period of time like for 100 of years, then you should buy a DNA storage kit and store your keys in it, I think you can't do it manually you have to take help from experts to convert your data into DNA storage strands. Well, this method is more reliable than other ones because it can last for thousands of years, Who knows in 3023, one of your generations might find that key phrase.
I suggest you, do not put too much weight on your mind to force it to remember keys, But on the other hand, i think it's also a good practice to keep your memory sharp and active instead of making it dull over time.
