I made the suggestion that they may be were mainly economic migrants because the OP seemed to assume that they were all refugees.

If they have been able to afford to get to Calais they are not the ones suffering most in the "apalling conditions in their home countries".

Don't just think of the Eritrean who could find the dollars to get to Calais. Think one the one who is stuck at home as child conscript or the child with no money who ran the risk of being shot crossing the border to a camp in Ethiopia before they reached the age for conscription and is stuck there pennyless.