How can Cleve's 1/r lower bound on the bias of coin-flipping protocols hold if parties can output random bits?
In a multi-party protocol, if every honest party just outputs a random bit, it's likely they won't all output the same bit and the protocol would be incorrect.

With two parties, the corrupt party can still bias the output. Suppose the corrupt party aborts in the last round whenever the actual protocol output would be 1. If an abort occurs, the honest party outputs a random bit. Then we have two cases, which each occur with $1/2$ probability:


Abort, output random $b \leftarrow \{0,1\}$
No abort, output $b=0$


Clearly the probability of outputting 0 is $3/4$, so there is still bias.