In the event of a fire in your home, a steel plate is recommended because it can keep the fire from destroying what you've saved inside. This is just another option for keeping your seed phrase safe. I believe that having multiple ways to save the seed phrase is preferable to having them all in the same place in case of fire or other disaster that causes you to lose them all or access to them all at the same time.
I don’t think memorizing a seed phrase will be easier than said. That’s a whole lot of random numbers generated and are not in accordance to any numerical or alphabetical order. Memorizing the seed phrase will be hard to keep long in the brain especially as you’re getting older by the day. Although, people’s brain functions differently, yours might hold for eternity while some can’t hold for even up to a month.