In practice, almost every implementation of Paxos uses multi-paxos. Even the "Paxos Made Simple" paper notes:
> In normal operation, a single server is elected to be the leader, which
acts as the distinguished proposer (the only one that tries to issue proposals)
in all instances of the consensus algorithm.
because otherwise you don't have a mechanism for ordering; the more basic Paxos protocol only discusses how to arrive at consensus for a single proposal, not how to assign numbers to them in a reasonable way that preserves ordering.
> In normal operation, a single server is elected to be the leader, which acts as the distinguished proposer (the only one that tries to issue proposals) in all instances of the consensus algorithm.
because otherwise you don't have a mechanism for ordering; the more basic Paxos protocol only discusses how to arrive at consensus for a single proposal, not how to assign numbers to them in a reasonable way that preserves ordering.