Indeed - I really don't understand their motivations. With a 4k$ product I really don't see them selling it at a loss, so they get paid either way and it should make no difference whether people are using third-party apps on it. If anything, it seems to be beneficial as according to the article people are apparently interested for this very functionality despite the price tag.
Unless of course the objective is not to make money selling a premium treadmill but to hit "engagement" targets to justify the next promotion or round of VC funding.