Hi Dear saad!
Well you know theorically you can increase the gain as much as you want. But in practice you are limited due to the Devices. In this case when you increase the gain and gain effects the output voltage, so the opamp have to support the load with more current. Unfortunately output current is not following and opamp would be overloaded. For example consider a 741u, maximum output current is only 25 mA. On the other hand output voltage is to be less than power supplies, you provide for opamp, i.e. if you support omamp with +10v and -10v you can not get more than +10v at output.
Thanks!