You can only say that for so few of them though? Lets take a look at the most irrelevant members: Koda, Sato, Hagakure. These are the only three in the entire class I would consider not having developed a true relationship with Deku, though he and Sato seem close due to making candied apples for Eri.
Who in the class besides those three have not been developed? Ojiro he established as someone who he respected in the sports festival, though I agree he hasn't much time with him since then. Tokoyami has plenty of set up and character on his own, and he and Midoriya clearly have a bond from the small interactions they have. Momo is in the same boat as Tokoyami, and but is clearly more focused towards her own confidence and ability than Deku's involvement in her life. Shoji I guess would be the only other one, but his respect for him, as he himself said, was set in stone back during the forest camp.
So at best, there are 4-5 class mates that he hasn't interacted with much or have any reason to be specially attached to on screen.
Now compare that, to his constant friendship moments and interactions with Kaminari and Mineta. Or how much he respects Mina and appreciates her for the dance lessons. Or Jiro, who had a whole arc. Or Tsuyu who has been with him nearly as long as Ochako and Iida. Or Aoyama who wormed his way into Deku's friend group and has shown how much his confidence has increased his own power and will. Or Kirishima who bro's out with Deku at any chance he gets, garnering enough trust from Deku sheerly through his connection with Bakugo as well. Or Sero who has had probably some of the most interactions with Deku out of the supports from the class. Bakugo and Shoto need no say.
So Deku has had very strong developments with at least 13 members of the 20 in class 1a, with maybe 2 of the 7 also having strong basis to really care for him, and only 3 being truly irrelevant to him.
How is that not attempts at developing a relationship?