Brake rotors already grooving

Less than one month ago, I replaced pads and rotors on all
four wheels. I've noticed that the front rotors already have
lots of grooves. I was careful not letting the new pads get
dirt or grit on them when installing, and everything was nice
and clean, as far as I can tell.

These grooves are not deep or wide, but I would have thought those
rotors would still be pretty damn smooth at this point.
The brakes work nicely and quietly, but was just wondering if
this was normal as it's been a long time since I've put new
rotors on a car. THANKS.

--
Cliff