One month security is never enough. Why not collect more?

[Mike Franco]

Most rentals in my area only charge security deposit equal to one month rent. They don't collect last month rent up front either.
Renters in my area have taken this for granted, and some are boggled by why I charge 1.5x rent.

1x rent is never enough. Once back rent is deducted, you have nothing left for damages.

If you're one of those who collects only one month security, what's stopping you from collecting more?