We are not permitted to choose the frame of our destiny. But what we put into it is ours.
I'm not sure why writing for others became harder. Probably a reluctance to give away anything you might conceivably use yourself caused a block. I did it, but it remained hard when it had once been easy.
I actually read 'Wonder Woman,' and here's the thing about her: she's more of a physical presence than anything else. You don't get to really know her on the inside.