16 April 2018
Instagram's Apple Watch app has now been discontinued after the availability of version 39.0 for the client app. It did not make an official announcement regarding the decision but if you will Instagram on your iPhone to the said version, you will not be able to see the corresponding app on your Apple Watch anymore.
The most plausible reason behind Instagram for Apple Watch discontinuation seems to be new Apple policy which allows only native apps to work on the smartwatch. It means all of the apps which rely on a connection/pairing with iPhone (aka non-native apps) to work have now been deemed as incompatible with Apple Watch.
It means if Instagram wanted to have its app continue working with the smartwatch, it would have to update and release it as a native app. It goes without saying that it would have taken some effort and time which Instagram did not seem to be interested in putting in. Additionally, it also possible that it might be working on a completely new Apple Watch app from the scratch which we might see in coming days. But as of now, there are no words from Instagram about the app's discontinuation or plans regarding the future.
It is worth mentioning that Instagram is not the only high-profile app/service to have dropped support for Apple Watch after the new policy. In the past, we saw the likes of Amazon, eBay, Slack, Twitter, and Google Maps following the same path instead of releasing a native app.