Just look at the Brexit vote in those areas and you may find your answer to opening up different cultures, truth is they just like thier own insular cultures, its not just culture?,, they are not really keen on Cardiff City Metropolitan folk anyways , ..
The reason why you see many more ethnic societies growth in Cities rather than Valleys , is work , housing , transport, easier transport access, weather more schools, health access. Its the same split in most Metropolitan areas the pull of the urban v the rural is the key ..
Ethnic societies tend to grow in the areas where thier forefathers first set up shop via the docks and Cardiff was in the forefront of those very early settlers.
Mosques in Ferndale town may never be a thing , however there are 64k Muslims in Wales 50 % in Cardiff ... 40 Mosques in Wales. So there is