Those pcb antannes must be carefully calculated.
Perhaps the manufacturer just copied the antenna layout.
Some of the 2.4GHz chips adjust themself to the antenna. I don't know if the Nordic Semiconductor nRF24L01+ can do that, but I assume it does.
Sparkfun decided against a pcb antanna, and use a chip antenna on the board: https://www.sparkfun.com/products/691
On Ebay, you will also find many boards with normal antennas.
Some people complain that those modules can only do about 30cm. Some boards have additions like LNA and claim they can reach 1000m. That pcb antanna could be good, if it was very carefully designed. But it seems that is not the case.
So what you have makes perfectly sense. If you want to do it right, buy a board with a normal antenna.