Can you explain why taxonomists suggested that the taxa containing birds and reptiles should be reorganised?

Ignore them. Cladists think that birds, having been derived from reptiles, should be in the same group. Of course, mammals derived from reptiles too. And reptiles evolved from amphibians, which came from fishes. By extending their logic, we should have all life forms in a single group.

o Because a crocodile is more related to a pigeon than it is to a turtle.
o Because the "reptile" grouping isn't monophyletic by dint of not including birds