It makes sense, when you look at other amniotes.
Sure, reptiles* show some signs of intelligence. Crocodiles use tools, monitor lizards recognise human faces, etc., those are all signs of cognitive capabilities. But it's simply not on the same level as your typical mammal or bird; it's like comparing a strawberry to a jackfruit, you know?
And yet, if these advanced cognitive capabilities we see in birds and mammals were inherited from their common ancestor, we'd see them in reptiles too.
*by "reptiles" I mean the paraphyletic group composed of the extant members of the clade Sauropsida, minus the nested clade Aves.