I thought it prudent to follow-up with EA to ask for an explanation for this omission. Does it have to do with the Switch and the way it works, or did EA simply not fancy it?
Unfortunately, EA's response is a frustrating mess that completely dodges the question.
"FIFA 18 on Switch offers Local Seasons allowing friends to play against each other across two consoles in close proximity to one another, and we encourage those looking to compete online to take advantage of online modes on Switch including FIFA Ultimate Team, Online Seasons, and Online Tournaments."