He came to that conclusion based on the constraints in his current situation. These constraints narrowed what he can do to solve the problem.
The first constraint in his situation is that he is very busy currently cultivating and will still be very busy in a year's time. He is just too busy to go around trying to increase his merits.
It doesn't seem like it would be a good use of his time because it will take a lot of time and effort for him to level up Mountain Karma and Mountain Foundation. He felt that it was a better use of his time to cultivate and increase his strength.
He wants to at least master the Everlasting Wood Art and some fighting spells before leaving seclusion. He believes that when he becomes stronger, it will be easier to earn merits.
The second constraint is that even if he decides to prioritize earning merits now, he doesn't have anything to do in the sect that will earn him merit in an efficient manner.
