Hi @Ankit Mathur , thanks for posting your query on Microsoft QnA.
May I know where are you seeing the option to buy a set of 100 licenses at a time , instead of 1 or 2?
To use and access WVD desktops, users must be licensed with an eligible user license. Per device licenses
are not eligible for WVD running Windows 10.
Eligible licenses acquired through all Commercial Licensing programs include the entitlement to virtualize
Did you get a chance to refer to this - licensing-brief-plt-windows-10-licensing-for-AVD.pdf
Let me know if this helps?