Because you are building glute muscles but keeping the fat layer the same size.
From the newsweek.com
You may be putting out only half as much work from one glute as with the other.
From the sacbee.com
I had been on Vicodin, but the pain from the tumor in my right glute was too much.
From the sfgate.com
Green has a right glute contusion and Moon had two wisdom teeth extracted last week.
From the usatoday.com
We do some jump roping and a lot of stability exercises for my glute and hamstrings.
From the orlandosentinel.com
Squeeze the right glute and hamstrings to come up and forward into the left leg lunge.
From the signonsandiego.com
Do FitFlops produce more glute and quad activation than regular shoes?
From the thestate.com
In fact, the strength difference between the left and right glute can be very significant.
From the sacbee.com
Was one glute in more pain that the other when you finished the testing?
From the sacbee.com
More examples
Gluteus: any one of three large skeletal muscles that form the buttock and move the thigh
, colloquial) A gluteal muscle
(Glutes) "Gluteus" comes from Latin which dates back to Greek meaning rump. Only other modern English word that might come from the same Greek root is "cloud" (and this is only a possibility). ...
(glutes) The muscles in your rear end. They're all important for cycling.