He is able to do many things but still stay as a neet, he truly wants to support his sister, i really belive that is th only reason he stays as a neet.
Even though Maruyama is trash I like that he asked for that when Haruko wasn't around and when sending her off he was actually kinda generous with letting her get something extra for herself and even encouraged her nicely. Plus he was more than willing to pay for that "thing". He's a lecher but he knows when to be a good person I guess
It's like the story: choose stuck in island with a mermaid: head fish or leg fish. Pervert will choose head fish (so they can use the leg), but smart will choose leg fish (you can still receive bj with the head)