I'm just going with Wynton Marsalis on this one; I don't have his pedigree, education and talent to defend that opinion as thoroughly as he could. Suffice it to say, while it draws on elements of the distinctly Black American mid 20th century art form called jazz, "smooth jazz" lacks most of the defining elements of what I (and Wynton) consider jazz.
At the end of the day, for people who like that sort of thing, that's the sort of thing they like, so no judgement from me. It's hard to argue with enduring commercial success.
It's not my bag, but i imagine some of the Latin jazz i like and make could get pigeon-holed as smooth jazz or easy listening. I still try to keep an edge on it, but I'm definitely not blazing trails by any stretch, so I probably misuse the term jazz myself by Wynton's definitions.