Opmap Based Linear regulator
May I know why I am not getting 10V at output.

You are not getting anything higher than 5 volts at the output because although the op-amp is powered from a positive supply of 15 volts, its output is clamped by the now forward biased base-collector region of Q1. See below and the little diode symbol I've added in red; it will limit U1's output to about 5.7 volts and, of course, that becomes about 5 volts at the emitter because both PN junctions in Q1 are forward biased: -

If you disconnected the collector from the circuit you should then see 10 volts at the output but, it's not much of a power regulator like this of course. If the 5 volts at the input (Vin) were sourced from a bridge rectifier (as per many supplies) then the bridge rectifier would get reversed biased due to the action of the red diode and the op-amp output would be able to lift the collector voltage with the outcome being that emitter would become 10 volts and hit the regulation target.