The Ending and The Sequel

[Lina]

So, I've noticed that a lot of people are worried about the sequel, while I was unsatisfied with the end of All Our Yesterdays. For Those of you who didn't understand the end (and I've also noticed there's a lot of you), here an explanation:

Young James killed himself, so Old James can't exist, or Em and Old Finn, because they (Em and Old Finn) were only the way they were because of Old James. Also, because Young James killed himself, and Old James doesn't exist, he (Old James)can't kill Young Finn or Nate, which is why they'er alive in the end. Marina doesn't remember any of this because Young James killed himself, so it can't happen, but it still did, so time fixed itself and essentially wiped Marina's mind of those memories.

What I don't understand though, is why can't there be a "shadow" of Old James to always give Richter the time machine formula, and basically have the future same as it was?