We may be unwilling to pay 50m for Cucu because we see him as a good option to rotate Cancelo and Walker, but not as improving our first XI. And maybe rightly so.
Cancelo is probably the most underrated City player on here. He's the only FB in the world who can be great both on the right and on the left. None of the top FBs in the league is versatile to that extent. Imagine Walker and TAA at LB or Robertson at RB. Plus, Cancelo is extremely fit and can play over 50 games in a season. The idea that Cucu comes here and is automatically better than Cancelo is incredibly silly.
In short, we have a LB, and he's the best in the league. Aganst weaker teams we'll play Cancelo on the right and the new FB (Cucu) on the left, against stronger teams we go with Walker and Cancelo.