Access is a great product that many are not using and don’t have it installed because they don’t want to spend the difference between Microsoft Office and Microsoft Office Professional (which includes Access).
If it were free many of those people would start developing databases in Access and then “get in over their heads” and would need to hire a software developer (like you and me - I looked at your profile)and we would create a more powerful database for them and eventually migrate them to SQL Server.
This would also create more work for us software developers and it would increase dependence on Microsoft (which I view as a good thing since I make my living with Microsoft).
It would spur otherwise unnecessary purchases of Windows licenses.