Because I have no motive to do so, of course.
Lying on a consumer poll is useful because they will accept me to take the poll, and awarded points, which can be exchanged for money. If I say I am retired, they will not accept me in the poll, and I will not get points or get paid.
No one pays anyone for taking a political poll.
If asked for my favorite Republican candidate, I might say Bachmann, because she is the most likely to lose. But I have not been asked, and probably will not be, because I am a democrat in most databases.
I don't consider it immoral to lie in a poll.