It is because it is a low-flow toilet functioning as designed.

Slowly pour a quart of water into the toilet bowl. If the water level doesn't rise, it should be good.

Check inside the tank and you will find a "Water Level" index either printed on the ceramic or embossed into the ceramic. Make sure you tank is filling to the level index. If not, adjust the float on your fill valve until you have the correct volume of water in the tank.

Next check the trap primer line, which is the small diameter plastic tube that goes from the fill valve to the top of the flush valve standpipe. Make sure the line is properly secured on the top of the standpipe to insure all water flowing through the trap primer line is in fact going down the standpipe.

If that is correct you are getting the correct supply of water to the bowl.