One of the problems with just taking Syrians from Calais (are there even many there?) is that a) it's extremely easy to get fake papers "proving" you are Syrian and b) once you're here, and your asylum case is challenged, it then costs a huge amount of public money to investigate and send you back if it's proved you're lying. So all it does is provide an extra source of income to organised crime and putting extra pressure on people to pay them - in order to defraud the British authorities.
I do Country of Origin stuff sometimes in disputed asylum cases (pro bono, before anyone jumps in to attack!) and one of my countries of specialism was previously super-popular with Arabic speakers seeking UK asylum. Over a period of five years, and multiple case, the applicant was never once from the country they claimed to be. In many cases, it's ludicrously easy to prove that they are lying. What happens is that I then submit a report to their lawyer, giving the details and also a suspected COI - and then I never hear again. However, since the migrant crisis, I haven't had a single COI request - which leads me strongly to suspect that people who are not Syrian are claiming to be so.
Interestingly, one of the other COI countries I am a link for - and afaik, the only person in the UK who is - I have never, ever had an asylum case to deal with - yet it has only experience about 2 years of peace in the last generation.
People want to come to the UK, as PP have said, because it's ridiculously easy to disappear into the system, even if you're due to be deported. You can work here, live many to a room, and even not being paid the minimum wage, you can stash for your needs and, in many cases, send money home - there are vast amounts of money going from the UK to, for example, India and Somaliland, sent from the "illegal" economy, and in the case of Somaliland, it actually has a significant impact at state level. Most people want to come here to work - they don't want to come and suck money out of the system: but it is helpful that our system is relatively unregulated (by European standards) and that in extremis, you can eg access free healthcare.