Cuckolding is a very specific fetish.
Cuckolding is not “your wife has sex with other people.” Cuckolding is “your wife has sex with other people as a form of humiliation play, for the purpose of erotic humiliation of the husband.” Usually (but not always), in a cuckold relationship, the husband doesn’t have other lovers.
Partner swapping isn’t humiliation play. The purpose isn’t to objectify or embarrass the husband.