The reality is, although it does maybe seem a little 'cold' on the surface, he has no responsibility to the McCanns. They're not his focus, CB is.
If they have a problem with his methodology, then they should be directing their criticism privately at the Met - their immediate info source, the police force actively engaged in their child's disappearance, the one Clarissa Dick says is in good and ongoing info-sharing partnership with the LE - and let them pursue it, rather than they themselves having a rather arrogant tabloid public go at HCW.
So yes, in answer to your query, I can completely understand HCW's lack of engagement here.