Manchin's problem is he's a centrist just to be a centrist. He has no real leverage in the Senate: he's not wanted by the GOP, he has no ideological connection to the party he's in, the Democrats, and he has absolutely no acumen for deal making. He and Sinema are fucking useless twits who offer nothing other than a vote.
The democrats have worked with centrists before, and sometimes they have success. The likes of Susan Collins have at least some ability to negotiate behind closed doors with both parties and, while working with them can be problematic, at least they have enough skill to keep conversations open to both paths. Manchin has done absolutely nothing other than string Democrats far enough along that he can effectively squelch the BBA because it's bad for his coal business. He hasn't reached out to any Republicans, he hasn't offered a constructive counter proposal to the Democrats that would at least give them a framework. He's even ignored his supposed constituents in the coal miner's union.
For all intents and purposes, Manchin is running out the clock on his political career.