Gang of Four - Entertainment

You mean the speak-sing vocals?

yeah

i know they sound more enthusiastic/shouty at times, but when they're at their more speaky

I'd probably figure it was just staying in what they knew they could do with their voice over those grooves. Devo, PIL Second Edition and Kraftwerk had similar vocals going on too. I think the grooves are so tight wound, you couldn't bust out and do a big vocal melody on it anyway, the beat is stiff.