AFAIK there's no way to diff/history of stored procs in the database (and certainly not against your VCS), so large companies usually do comment blocks at the top of each one.
Sqitch, go check it out. Versioning database code with linear migrations always has this issue, you add a column and where's your diff on that without going through your list of migrations. Stored procedures are no different, and the sooner people use better tools the happier they will be with maintaining their database migrations.
SQL is a terrible general-purpose programming language by the standards of today, which makes it a terrible way to express business logic.
In a smaller company, those barriers aren't really meaningful. In an enterprise, you're easily adding a week or more to change control process to ship.
I think another factor towards why database focused solutions aren't popular in small companies is that MySQL historically hasn't been the best platform for that approach, and you need more expertise to scale the database.