Apart from mathematical theory, is there any evidence whatsoever that multiverses exist? Do you not think that it is an attempt to give an alternative (but fanciful) hypothesis to respond to the FACT that our universe is not only incredibly complex but beautifully "designed" with everything "just right" and with the constants and equations all in harmony and fine tuned?
Bob has been rolling dice all day long. Thousands of times he's rolled his handful of 6 dice. He's come up with all sorts of combinations and scores, all throughout the day.
You walk along, and see that he has rolled a set with 1,2,2,3,3,6. That's your grandmother's birthday - December 23, 1936! It has special meaning to you.
How amazing is the FACT that these dice are perfectly representative of your grandmother's date of birth! It must be by design!
You haven't observed the tens of thousands of tosses that Bob threw before you showed up. You don't stick around to observe the tens of thousands he'll toss after you leave. You happened upon one specific observation... and from that you concluded that the dice were specially designed
just for your enjoyment.
The fact that a particular combination has occurred does not in any fashion provide information regarding what other combinations could have occurred, nor doe sit in any way imply that the specifically observed combination is in any fashion "special", let alone "designed".
ETA: I'ts kind of like being amazed by the "skill" of the middle-schooler tossing a basketball over his shoulder and making a basket from the other end of the court. Never mind that he actually spend 7 hours trying that same move over and over, and deleting all the videos of his failures. You see the one success and conclude that he is just wicked skilled, yo! Totally amazing!