is remembering 12 words that hard?
It's not.. until it is. Just imagine a stroke, or a (motor)bike crash, or many other things the can happen to you.
Plus, mind is a very strange thing. In a year or two you will be certain the 5th word in your seed is "about" and in reality it was always "above".
So no. It's not difficult to keep in mind 12 words for a while. But the longer that while is, the more chances for something to go wrong.
Stroke affects short-term memory more than long-term memory. And if you get into crash or get a heart attack, develop dementia or something terrible happens, the first question is if you survive and the second question is, if you actually remember that you have bitcoins or in best case, where you saved your seeds.
Memorizing isn't that hard or bad practice. If you try to memorize seed phrases every day for multiple times in a one year timeframe (keep seeds for some months or one year), if you write them down very often and then burn that paper all the time for security purpose, or if you write them down on keyboard (unplugged from computer), then you not only depend on your just memory alone, you also seal it deep inside your muscle-brain memory, you touch the keyboard and your hand know what to write.
By the way, if you try to memorize 18 or 24 words, then you shouldn't trust your mind in this case because it's too much to properly remember for a long period of time. 12 words are fine!
In my school, emphasis was on memorizing of information, probably that played its role into making it easier to memorize things.