Why do designers use op-amps with fractional gains?
The opamp functions as a buffer, providing a much lower output impedance than the bare divider would have. This completely eliminates any loading effects created by the downstream circuitry.

A noninverting voltage follower configuration would provide the same benefit (and the same downsides), but if you want the inversion, this is the way to go.

Also, it is sometimes important for the application that the node between R1 and R2 be held at ground potential.