I get what you're saying, Timo, but the episode does not say in any way that changing course would not avoid the collision. All they say in the episode is:
If you're right about this...
perhaps we could escape the loop
by avoiding the collision...
That's our guess.
Maybe we should reverse course.
For all we know, reversing course
might be what leads us into the
Picard thinks a moment, then shakes his head.
We can't afford to start
second-guessing ourselves. We'll
stay on our present course until
we have reason to change it.
In the meantime, let's do
everything we can to avoid a
They just somehow assume that changing course will do nothing. No explanation is giving for this decision. We can come up with fanwank explanations after the fact, but it doesn't matter. Our speculation isn't canon, and there's no logical reason why they shouldn't at least TRY. After all, what's the worst that could happen if it fails? They'll crash and get stuck in a repeating timeloop?