I only know about it because it gets posted to reddit every 3 months and makes the front page.
But evidently, in order for Zemeckis to get the opportunity to make the movie, he had to take Stoltz as the lead. Eric Stoltz was just coming off of Mask, which was a huge hit, and the studio wanted to make him a star. But Zemeckis got them to agree that if the early results weren't satisfactory, he could replace him. So, you could imagine that Zemeckis probably didn't put him in the best position to succeed or bend the script to fit his strengths. He probably always intended for Stoltz not to work out.