No messengers exist as an app on any smartwatch, so you won't get any Wear OS WhatsApp, Instagram, Telegram (and whatever messenger) app versions. The only way to interact with them is via the phone by pushing the notifications to the watch, which allows you to respond. But that's all that the watches are good for, because who on earth would want to use such a small screen to read through entire conversations?
So, unfortunately for you, they don't exist as of now and they probably never will.
And another thing: If you had too little space, the watch would inform you when trying to install any app. So they would still show up in the search results, but you just wouldn't be able to install them. Which means: Should an app not show up in the Google Play Store search, it simply doesn't exist. There's nothing wrong with your watch.
Should you desire to uninstall any app that isn't qualified as a system app: Just go to the app drawer and long-press the app you want to uninstall. It'll show you the option to uninstall the app if it's not a system app.
