Most likely because Lenovo has made it impossible for you to Overclock a laptop or make any physical changes that could end damaging the computer.
It is no problem Overclocking a GPU or CPU in a Desktop, But a laptop you should never overclock due to the fact the Laptop specs don't take into account the huge amount of heat and power the Overclocking will produce.
Need to contact Lenovo Support and ask them if your laptop can be Overclocked. Most likely they will say no.
