Just because there are representatives doesn't mean that these representatives will always be in agreement. On top of that, since Islam is what we call a "desert religion". Much of the emphasis is put on the individual, so the individual is not always expected to tow the "company line". Same is true in Judaism with the exception of the chasidim. OTOH, Christianity tends to more emphasize conformity, which is why there are roughly 30,000 denominations.
But you strangely don't wonder why the Jewish UCEI signed while the Islamic UCOII didn't.
Coincidence?