@maaniwild
While WGTShamWow has done a good job of addressing this, I'm just going to add a few things.
First, surveys take your demographic information up front because I suspect they're all using some variant of a quota-based sampling scheme. As the post above notes, they're looking for certain demographics. It's both to your and their advantage to do the demographics up front. It actually saves you time.
Second, if you're not already doing so, you should use a "throw away" email account for surveys. Just create one on any number of different free email providers.
Third, I've actually used one of my regular email accounts for some surveys, even though I have a throw away email account. I haven't seen an increase in spam. Indeed, I get very little spam to that account, and none of it is from doing surveys. By the way, over the last couple of years, I've completed a lot of surveys.
For the most part, the surveys under the "Take Surveys" tab are legitimate. Yes, I get screened out of a lot of surveys. But I also complete a lot as well.