What if someone enters a shop with explosives, or the bus station, or a mosque, or a hotel, or where ever? You can't have scanners everywhere.

The scanners at airports are to check you aren't trying to take illegal items onto the plane.

And even before the scanner was removed you could still have walked into the airport building and blown your self up if you'd wanted to. There was a good stretch of room before you reached the scanner, and it was often full of people queueing.