Except Islam’s spread into Asia occured chiefly through maritime trade. How else do you get your religion to modern day Malaysia? 
Islam wasn’t terrible interested in exploring the new world, but it was perfectly willing to be carried across the ocean to regions that were already known. As it made its way east, it kept entering into new areas of trade relations, “port hopping” as it were, down the coast and eventually into Southeast Asia. No blue water sailing was required, just lots and lots of coastal work.
