I don't know about visas or stereotypes (after all Africa is a range of cultures and many of men are European even with African roots). This just comes from stories from many women over years.
We have room for growth. From my observations US doesn't have these issues, but I might be wrong.
In the USA, the largest percentage of black women dancers I have seen in salsa were in NYC. Compared to any west coast cities as a percentage and absolute numbers too, NYC always has larger number of Africa American dancers. I have no idea how it is in Chicago, Miami, Atlanta. I don't think women of any ethnicity can claim to get more dances or not get enough dances in the USA.
I have verbalized like it several times and also mentioned a few times how I hardly encountered followers with African roots in EU. May be Paris and London are relative exceptions. That is not an issue with the leaders. The leaders with African roots tend to be fairly popular in both salsa and kizomba.
With the performers from Cali, Colombia I also observed that there were far more make performers of Afro-Colombian heritage than the females. Among the couple performers from Cali, the followers would be overwhelmingly non-Afro-Colombians. On the leaders side I didn't notice as much discrepancy.
This is first time I am hearing that the black women in EU don't get asked as much. If that is true then it explains their extremely low numbers in EU salsa.