Is there a reason why more OSS projects don't follow this model? It sounds like you are saying that there are clear advantages here that other OSS projects lack.
There are business models that work for the extraordinarily popular open source projects (Linux, SQLite, etc.) that don't work for the "well-used piece of infrastructure" projects, even though that category is very important in aggregate
Because at that point it's not a 'project', it is a full business.
SQLite is arguably the most widely deployed database in the world. It also has its roots in government/defense contracting so it was built with navigating that kind of red tape in mind.
Most OSS projects simply don’t have that kind of weight or discipline to follow SQLite’s footsteps.