I would say there was some improvement In the last third of season. He wasn’t crashing anymore and was consistent in the time difference (more or less) to albon as well.
On top of that, we just don’t see the data the team is seeing when it comes to an improvement.
One other thing to keep in mind. There is a supposedly very talented new driver starting in F2 next year that could drive for Williams in 2025, so that could play into the decision as well. Although I just looked for it and couldn’t find it. I think Alex Jaques talked abiut it in the last F2 sessions.