Why the emphasis on the RC church and not on Islam? The emphasis on the RC church is basically the tactic known as negative advertising. The RC church is Watchtower's greatest competitor and former/disaffected Catholics is Watchtower's greatest market. So it makes a lot of sense to them to bash the RC church.
Muslims, on the other hand, are not very amenable to Watchtower conversion. Unlike the Catholics, they use a different holy book altogether and their religion teaches them that the Bible has been changed by men and cannot be fully trusted so all the JW religious propaganda that is based on exploiting people's respect for, and deference to, the Bible - it's useless on Muslims. Watchtower has to work twice as hard to convert a Muslim than to convert a Catholic. They first have to convert the Muslim to trust the Bible before they can convert them to join the JW religion. It's just too much work. As a result, Watchtower is not too eager to bash Islam because they don't stand to benefit from doing so. Additionally, Islam-bashing could potentially stir up radical Muslims clerics to issue Fatwas against Watchtower resulting in JWs in Muslim lands being attacked and the religion being banned in even more Muslim lands than it is already.
Bottom line: RC bashing has never been rooted in genuine indignation for the wrongs of the RC church. It has always been a form of negative advertising geared toward stealing easy sheep from the RC market. Because it's so difficult to get sheep from the Muslim market they have zero interest in bashing Islam.