Update: We've tested Nintendo Switch Sports on the Switch Lite with some Joy-Con (you can download the playtest app now, but you can't actually get into any games) and it does seem to be another case of Nintendo being overly cautious here to avoid disappointment.
You can use Joy-Con to play Nintendo Switch Sports on the Switch Lite, but it naturally won't be the preferred approach to play; Nintendo is perhaps keen to make sure this is experienced on a big-screen TV with plenty of room for Joy-Con swinging, and not on your dining room table with the Switch Lite propped up by a pile of books.
We've approached Nintendo for an official statement on the matter, and will update this post as and when we hear back from them.
An online playtest takes place this weekend (although it's one you can't talk about freely), but one aspect that hasn't been widely publicized is the fact that the game cannot be played on the Switch Lite, or more accurately, the game doesn't support Handheld Mode – only tabletop and TV mode, according to Nintendo's official site.
This might sound like stating the obvious – the Switch Lite cannot be connected to your TV and lacks removable controllers as standard (although you can still pair Joy-Con to the console) – but it's something that has perhaps slipped a few people by: