I would assume that “market share” is related to the relative number of units sold/number of active subscriptions/fraction of total sales in terms in revenue, or some similar metric. I run a variety of different distributions on servers (bare metal, VMs and containers) and desktop computers. Do they all count equally? Without giving it more thought, I wouldn’t even know how to determine the market share of Ubuntu in my own home in a sensible way.

With Windows, I can just count the number of active licenses. Oh wait, its zero.