It's really simple, Martinez can't survive with the players he had at Wigan, and he also can't bring the results that match the quality of players we have.
All in all throughout his career, he never manage to bring the best out of the players he had no matter which team he manage. His team will never be able to play at 100% of thier capability never mind 110%. That explain why we are struggling to cope with teams that are on paper inferior to us. Our opponent play at thier maximum while we stroll around and defend expecting to get the ball back without putting in a challenge.
I'm surprise he can stay in this industry for so long.