Let's say we have an egg and a broken egg. As we know, the broken egg has more entropy.

Now we put the two eggs in two bowl and whip them hard.

Voilà, the eggs become macroscopically the same. One of the macroscopic properties is entropy.

So we can conclude that gravity is very good at beating up matter.

And matter has a limit of how beat op it can be. (Bekenstein bound)

So, the two aphorisms above are the answer to the question of why two black holes with the same mass have the same entropy.

Let's say we have an egg and a broken egg. As we know, the broken egg has more entropy.

Now we put the two eggs in two bowls and whip them hard.

Voilà, the eggs become macroscopically the same. One of the macroscopic properties is entropy.

So we can conclude that gravity is very good at beating up matter.

And matter has a limit of how beat up it can be. (Bekenstein bound)

So, the two aphorisms above are the answer to the question of why two black holes with the same mass have the same entropy.