then that's another problem. almost always, these two can not be achieved together.
people aren't known to be able to create strong passwords. to be able to remember their passwords they always end up with weak ones that could be guessed in most cases.
and if the password were strong (truly random) then it can't be memorized over long term. they still have to write it down so that they won't forget it (after like in a year), and if they are writing it down then why not use the method that is already tested and is considered safe meaning BIp-39?