"Why doesn't Apple Calendar have automatic birthday reminder or celebration features?"

It does. Go to Settings > Calendar > Default Alert Times > Birthdays, and choose the time you want to be alerted. If it is set to None, you will not see the reminder.

You are welcome, the Calendar app has always had the ability to remind you of Birthdays. That is also why you have a specific Birthday calendar in the app so you do not have to set individual reminders for each of them.