Little bit of inside baseball here. One challenge is they would have to pick a new candidate prior to the convention, in order to meet the filing deadline to get listed on the Ohio ballot. It is not likely they win Ohio if people have to write them in. So they can’t just go to a brokered convention and hash it out in realtime.

Secondarily, per campaign finance regulations, they cannot just dump the ticket and then transfer the campaign cash to a new slate of candidates. If Biden were to step down, they’re stuck with Harris, otherwise they cannot use that money. If they somehow convince both to step aside, they have to raise all new money to finance the rest of the campaign, and the time between the convention and the actual election is not a lot of time to raise money (let alone use it wisely).