The thing is there not being more viera mixed race kids is kinda wild because in their lore the ones we see outside of their homeland are self-exiles, there would be tons of viera having kids with other races as the self-exiles are also the most wanderlust and spread far across the world. Even in the First this is kinda how they're treated. It also feels less like people view the mixing of people being bad and more the circumstances of the unions.
Spoiler for HW and StB
Hilda was the lovechild of a highborn Elezen and a lowborn Hyuran maid, this would immediately be a cause to become a social pariah because it was an affair in a society that is extremely aristocratic to the point noble families trace their lineage to ancient founders with pride
Arenvald's entire story around his mother also portrays his mother was forced into the relationship, which taking people in a conquered nation as a wife as a trophy was quite common throughout history, she never really viewed Arenvald as something she wanted and at one point tried to carve out what she believed was where Arenvald's third eye would be.
Throughout the entire game we're shown that no society is truly just one race or culture (which even in real life was often not the case), so these intergrained societies made up of numerous races wouldn't just not have kids together, it wouldn't make any sense for them, we even see numerous times of couples where the parents are different races or people being into someone of a different race.

Originally Posted by
Mostly_Raxus
the game need laladyns.
for science.
(pray the dad is the lala...)
Tbf we do see two prominent characters being incredibly into each other, one being a Highlander General and the other being a Lalafel sultanate.