They're so good for each other.
I think the key is that they were both brave enough to stick their necks out the first time. The manga standard is that they never even manage to do that, so they never get any positive feedback and can't move ahead. But these two both took a chance and made themselves vulnerable, and it worked out for them. They're still scared and insecure, but in the end, they manage to ball up their courage and go for it, and it keeps working out.
And I'm pretty sure they just got their first in-universe shipper.