Your point is true, though the positive impact of it won't be felt until 2027, which is why it is not a headline.
If they designate Carr as a June 1 cut a year from now, they will still have to carry his huge cap number to May 31, 2026 which is beyond free agency when the use of that money could apply best. The plan may be to leave 2026 with a good amount of cap money to turn over to 2027. Another benefit is that after June 1, 2026, they could do deals with players they want to sign 2nd contracts with.
Unless I'm missing something, you are bringing attention to a good strategy option for helping more... in 2027.
Maybe Carr does well next year or does not do well. I just don't think Kellen Moore cares because Carr is not Matt Stafford and he is not going to be Moore's QB long-term. I would think that Moore took the job with assurances that if they keep Carr, it's for a year, and they will not hold Moore accountable if he craters.