I don't think there's any evidence beyond wishful thinking, though, that this would discourage people from coming. For example:
1. Desperation drives many, so why would that change if there's a risk of being sent to Rwanda?
2. Even if it enters their thinking, many might chance it anyhow because the risk of being caught is, or is perceived to be, low enough to cross.
3. Why are migrants expected to know so much about the ins and outs of UK Immigration policy? Many might not even be aware, or might not take it seriously, or some such.
4. And, finally, the number that was intended to be sent to Rwanda initially was on the order of 200 (
https://www.telegraph.co.uk/politics/2022/07/22/rwanda-can-hold-just-200-channel-migrants-cant-stop-returning/ ). While that maximum may rise, it's obviously up to Rwanda how many they'd offer to (or be able to) take. But the number coming in on boats was about 45,000 last year, and is expected to be similar or higher this year. So on that basis some might come anyway because even if they're caught the odds of being sent to Rwanda are still low (less than 1%).
My comments earlier about the lawfulness of the policy still stand -- let's see what the Supreme Court says -- but the idea that this would be some kind of magic bullet was always nonsensical.