Hi,
Thank you for writing to Microsoft Community Forums.
This issue could occur when distros are not stored on your system driver or if your system is in lower build and also if Windows Subsystem for Linux is not enabled, you can follow the instruction from the article Windows Subsystem for Linux Installation Guide for Windows 10 and check if this helps you.
You can also Manually download Windows Subsystem for Linux distro packages and install it.
If you need any further assistance, I suggest you to post your query on TechNet forums where you will find support engineers who are well equipped with the knowledge and help you fix the issue.
Hope it helps,
Amit Sunar
Microsoft Community – Moderator