Theres a big difference between being well known (meaning only hardcore fans) and famous (meaning general public). Even a legend like Dekker would be unknown to the majority of the public. The only names that people know are the ones that they see compete, the only ones they see are the ones with TV coverage. Alot of people will know the names Sefo, Hoost, LeBanner, Sapp etc, fans will know Kaus, Chapman, etc, but theres probably only 2-3 people in the southern hemisphere that have heard of Villiame.
Most likely with his 50 fights hes still only making small amounts of money (especially with only 3-4 fights a year), sponsorship might make up the difference but really fighters need to head to where the money is. TV coverage = money, TV coverage = fame, fame = sponsorship.
K1 and SL will have massive shows, TV coverage and more international recognition. That is exactly what Villiume needs if he wants to move from being well known to famous.