According to an official statement issued by Instagram to French blog iPhoneAddict (translated and quoted by ZDNet's Jake Smith), "The Instagram app for Apple Watch will no longer be available as a stand-alone experience once users upgrade to Instagram version 39 on iOS, released April 2, 2018". Don't worry, you're not alone. Since that time, users using watch to view the photo feed, and leave "likes" any publications. However, the app was never updated with video support or LTE connection. Starting April 1st, all Apple Watch apps must feature watchOS 2's SDK development frame work or later, with new apps only being allows to utilize watchOS 4's SDK.
It comes as a sad news for Apple users, as people will not be able to use Instagram on their Apple Watch. The challenge seems to be judging adoption of apps today with the poor reception the initial wave of apps received on the dramatically slower first-gen Apple Watch.
For apps like podcast players, creating a truly first class experience isn't possible today due to limited developer resources - Apple's apps have more privileges than third party apps - but messaging and social network apps have proven useful on faster Apple Watches. While Apple continues to push app integration with the Apple Watch, the device has slowly evolved into a fitness and notification-focused wearable.