"keeping compatibility with a large user base"
Most users don't look for an OS - the look for applications to perform what the need or like.
And they may not want to abandon them just because someone in a marketing department decides they should not run anymore, or have to be bough from a store to get a 30% ransom, or need to have a new UI to match the latest fashion.
One of the reasons Windows kept its market its exactly because of its backward and forward compatibility - you could usually run new applications on older systems, and old applications on newer ones, within reasonable limits. So you can decide what to upgrade and when.
Kill this, and make it a fully consumer system with built-in obsolescence, and many customers will look elsewhere for systems that don't force them to chase the latest fashion at all costs - especially at higher costs...