Well, it’s possible that all the rooms were designed by different professors with little to no cooperations so that one single breach would not compromise the security of the whole thing. If Snape wanted to put claymores in other rooms, he’d need to tell the other professors.
And if this is possible (I have no idea whether there is a ‘detect claymore’ spell) then the other rooms could have had claymores too.
Well, it’s possible that all the rooms were designed by different professors with little to no cooperations so that one single breach would not compromise the security of the whole thing. If Snape wanted to put claymores in other rooms, he’d need to tell the other professors.