Despite a myriad of translation engines and web sites, human translation is still a very important job that requires a lot of experience and knowledge to be done properly.
It’s not just the language.
No-one in their right mind should tackle e.g. legal or technical translations if they’ve never worked in any of the fields (unless the job pays really, really well and it’s worth digging through books and Googling everything :)).
Translation work is well paid (and rightly so) – and thus quite expensive for the client.