They probably know all of their regions' Pokemon beforehand and send you on your journey without the knowledge because it makes it all the more exciting for an adventurer like yourself; just full of surprises. Where would the fun be in a Pokemon journey if you just went around already knowing each and every one that you meet? Pokemon also have a bunch of different habits, so it could also be to make sure that even more possible data is gained and stored incase someone new happens to get involved in a situation where unknown habits, etc turn up.
That's something that used to bother me once I started getting more and more into the games, but this is how I ended up feeling about it, haha.
Or who knows...maybe it is some huge troll all of the regional professors are pulling off.