I updated my Nokia 8 to Oreo 8.1 beta, and while going through some settings, I noticed that Android System WebView is disabled by default, and cannot be changed.
Why is it disabled?
Even though I noticed it only now, the change was introduced in Android 7 Nougat itself. Chrome will take over its place.
Read beeshyams answer for further info.
If I go to apps manager and disable Chrome, then the Webview app is automatically enabled, and can be updated from Play Store.
If I enable Chrome, WebView is automatically disabled again.