Why so desperate to reach the UK?

This BBC report says that the 'migrant' are desperate to get to the UK but doesn't really ask why. Only Keith Vaz is quoted re this angle:

'Keith Vaz, Labour chairman of the Commons Home Affairs Committee, said the migrant situation was the "biggest crisis" facing Europe.

He said migrants were trying to reach the UK because "it's the country they think they can work in illegally".'

No mention of our excessively generous benefits system?