[Goldmine]

From my observation, those that converted to Islamic religion are all because of marriage to a Muslim spouse. It seems like Muslims will never convert to other religions for the sake of marriage.     

Yes! I agree. Thats my observation too. And if they do, their family or their guidance or religious leaders will protest by saying their children are coerced, brainwashed, confused, tricked, not knowing what they are doing and incapable of making the right decision. Others cannot convert the Muslim but Muslim can. 
Islam is a very sensitive religion.