why a solutions in different concentration has the same pH ?

In theory, the pH values of 1M HCl and 10M HCl are not the same. The 1M HCl should have a pH of 0 and the 10M HCl should have a pH of -1. If you try to measure that with a pH meter, it may be problematic because the pH meter may not be able to display negative pH values and so both show 0 for the pH. A second problem can arise with the choice of the pH electrode. Some electrodes may not reliably indicate pH values that low.

A second problem has more to do with the chemistry of HCl than the ability to measure the H+ concentration. As the concentration increases a phenomenon known as ion-pairing increases. It's not the same as H+ and Cl- recombining to form the covalent bond and make HCl. It is an elecrostatic attraction that may last for a very short period of time before the H+ and Cl- ions move on to other partners. But it is enough to "confuse" the ability of a detector to measure accurately the hydrogen ion concentration. Due to ion pairing, the 10M HCl hydrogen ion concentration will not be much different from the 1M HCl hydrogen ion concentration.

They will have DIFFERENT pH values, not the same.

ph is -log(h+)
In 1M H+ is 1 and in 10M H+ is 10