I'm not quite certain what Peter May had in mind 40 years ago, but probably he had in mind the fact that pushouts are a lot better behaved in CGWH than in CHGCGH. Specifically, CHWHCGWH is closed under pushouts, one leg of which is the inclusion of a closed subspace. CHG CGH does not have such nice behavior, and pushouts like that are used all over The Geometry of Iterated Loop Spaces, specifically in the construction of a monad from an operad and in the use of geometric realizations of simplicial spaces.
CHG would be "compact hausdorff generated" instead of "compactly-generated hausdorff" - this is a case where the letter order matters
David White
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