I think perhaps the lack of conversion in some Muslim societies is possibly due to restrictive laws about that.
Muslims in the West, where there are no such laws, are
starting to convert, although this phenomenon is far more common in some communities (especially Iranian Shiites) than others.
There haven't been very many (if any) Somali converts in my area, but it's probably only a matter of time. One thing I've noticed is that second-generation Somalis seem to be gradually assimilating into broader African-American culture (listening to R&B and hip-hop music, etc.) and are no longer as isolated. Some have taken up smoking (which in itself isn't a good thing, although it does imply they aren't as devout in their Islamic practice).
This makes it more likely that some of them will leave Islam; a Muslim who knows only other devout Muslims is far less likely to convert since doing so will leave them completely friendless.
The Hmong, who have been here about two decades longer, now seem to be split about equally between Christianity (there are numerous Hmong Protestant churches, and even a few Catholic ones if I'm not mistaken) and the "old country" faiths (Buddhism and shamanism). The same will likely happen to the Somalis, it's only a matter of time.