Why is that weird? Attorneys in this are working on behalf of the US Government. If they feel like settling gets the best deal for the government, then they do that.
It can give the feel of extortion. Settle or else. There is quite a window where settling -- even when provably innocent -- is easier/cheaper than facing an agitated prosecutor.
Settling has nothing to do with a finding of truth.
Do you have any evidence to base this on? Robinhood could easily afford to go to court if they felt the evidence was on their side. $65 million is probably more than what they've ever made in profits, so if they can pay it off without blinking, chances are a court case would result in an even larger fine.
On the same token, it's doubtful that the SEC would proceed to charge Robinhood if they knew they couldn't make the case stick in court.
Settling has nothing to do with a finding of truth.