Back in the day. 60's 70s, Cayenne was classed as THE ONLY chilli powder in the UK.
Generally speaking, there was nothing else available for most English folks.
All the recipes, and books referred to it by name.
A bit like only being able to buy Olive Oil at a Chemist.
E.G. If Utube early vids, like Madhurs first Indian TV series, she explains spices
and Cayenne Pepper and doesn't mention Chilli powder as such.
Evolution
cheers Chewy