They're back together, yes, but the relationship is built on lies. Furthermore, the troubles that they overcame to be together, the on again off again they've been referrencing for the past decade, all happened off screen, so there's reason to be invested. Why care about people getting together when you haven't seen what they went through to get there? We cared the first time because we saw what they went through to finally find each other, and the work they put into the relationship.
Marvel and Spencer are laughing at us, cashing in on nostalgia for MJ/Pete while not putting in the work to actually make the relationship rewarding. I'd rather have MJ gone for good than see this debased and tainted money grab.