Let's be accurate on a few things.
Lance was drafted because the team saw him as a *great* fit for Shanahan's offense, that was well documented.
He was given every opportunity to be 'the guy' and got outshone by a lowly draft pick, literally the lowliest possible. The fact that the Niners went with Mr Irrelevant proves that draft status played zero part in Lance's fall from grace. It's a meritocracy in the NFL.
And the NFL has proven time and again that if you get injured, they don't hold your spot for you. When you come back, you either earn it or you don't. He didn't.