Could also be reverse: why pay for software that won't run on your computer anyway?
Absolutely, that's a calculated decision that companies make. It is fully expected that a certain market segment is not interested in being a customer at a given price point. Market segmentation is often done by OS version or device hardware profile.
Or for free software, chances are it is add supported. So push as many ads and trackers until the churn rate gets too high or competitors take market share.
Or more generally, maybe the design just follows the money.