With regards to why some, and not the vast majority, want to come to the UK, there can be many reasons.  Many speak English, have visited the UK on previous occasions, have family here, see the job prospects as good, see their best chance of a bright future being in the UK.

Once the decision to flee has been made and acted on then other factors come into play other than just survival - yes placed in a camp in Greece or Turkey the likelihood is that they won't die but just staying alive is not something any of us want.