Operational Amplifier Virtual ground
I know that Opamp trys to hold the input voltages the same


Not quite.  The correct statement is

"When negative feedback is present, the voltage across the (ideal) op-amp input terminals is zero"


  why we're not getting a virtual ground on the + node if we connect -
  node to ground?


In the typical configuration, the op-amp output is connected in some way to the inverting input and, for the ideal op-amp, the output voltage will be whatever it needs to be such that the inverting input voltage is the same as the non-inverting input voltage.

If one grounds the inverting input instead and connects the output in some way to the non-inverting input, it is true that mathematically, one can show that there is an output voltage that will make the non-inverting input voltage zero.

However, it is easy to show that this is an unstable situation - positive feedback - and that if the non-inverting input voltage is disturbed, the output voltage 'runs away',  amplifying the disturbance rather than attenuating it as is the case with negative feedback.