At one point, both companies were about nostalgia and shock value. But the difference is that Marvel had changes in leadership and they were able to keep both old and new characters as well as making their B and C tier characters into households. In the words of Jim Shooter 'there is no first string or second string, everybody's first string'.
Miles, Kamala and Kate also all have the full backing of the Corproate Disney backed Marvel Machine. Jaimie and Virgil are lucky if their respective projects managed to show on screen and if their appearances continue beyond that.
That's an oversimplification. There is a lot of factors at work here.
In other words, Batman is a band aid. And the reason why he became a band aid is for the reasons that Bruce Wayne stated; all the other franchises have been driven to the ground while Batman remained more consistent, stable and a world onto itself.
A lot of elements that make characters unique have been filed off with multiple variations and origins of a single character and an inability to move beyond a specific set of stories. How many times are we going to rehash Killing Joke or Raven dealing with Trigon or Superman not doing enough for the planet or WW killing Maxwell Lord? There is also a confusion on who or what characters are supposed to be. I see Warrior Woman-Daugther of Zeus WW, bland goth Zatanna, Khalid Fate, sexy Lobo, dead mom Barry Allen and it's like somebody at marketing dreamed them up.