After Meursault arranged for his mother to live in a nursing home why did he visit her so infrequently?

Meursault's infrequent visits to see his mother show how little he has in common with others. He is alienated from other people, including his only family member. Simply put, there is no reason for his not visiting, but this lack of a reason permeates more than his relationships. From his perspective, to visit and not to visit may not seem so different. Meursault has few preferences and sees no reason for differentiating between things that might usually be considered obvious or common sense. This same absence of reason and indifference to social norms also make it impossible for Meursault to answer why he killed a man. The "best" answer might seem obvious to his lawyer, but like with the question of visiting his mother, Meursault is uninterested in attaching himself to any reasons. He is, instead, more focused on the awkwardness of the nursing home patients and the blinding light of the sun.

Meursault is a nihilist. This means that he doesn't believe in anything, be it God, love, or country. It is not surprising, then, that he is so emotionally detached from everyone, including both his girlfriend and his mother. It's not so much that he hates his mother; he simply can't feel anything for her, so utterly indifferent is he to every other human being.
Meursault's cold, unfeeling attitude towards his mother becomes an important element in his murder trial. It soon becomes clear that Meursault is not simply on trial for killing the Arab at the beach, he's also on trial for his nihilism and his total refusal to conform to society's norms and values. It is instructive that Meursault's lack of grief at his mother's funeral is cited as evidence of the threat he poses to society. In the trial it begs the question of what kind of man doesn't cry at the death of his own mother? It is also somewhat telling that Meursault's relationship with his mother is regarded as of greater cultural significance than his murder of the Arab, thus revealing the deeply ingrained racism in French colonial society.