The exchange is not always enough: with a protected knight, a blocked pawn, and the defending king close, the rook has no entry squares and no second target. Knowing when an exchange-up position is only a draw is as important as winning the winnable ones.
Change the bishop of the previous drill into a knight and the evaluation changes to a draw. The knight on e5 is protected by the king on d6, it covers the d3 pawn's advance square (nothing to cover, but it covers f3, c4 and the approach squares), and it cannot be attacked from a distance by the rook without the king being able to reinforce.