why do the games never acknowledge character bdays?

the vast majority of party members have canon birth dates, and I find it kinda odd that in games that so heavily feature bonding activities between you and your friends that these kids don't even mention their birthdays. I get that it could conflict with time management but why not have some optional birthday event if you've unlocked a teammate's social link? that'd make it so not all of them are available but it'd be more reasonable than nothing. let's say you could get some birthday cake item that has super strong healing or smth.