To stop robots, scammers, hackers, and people that would try to manipulate the poll. It also goes through a legitimate well respected third party for payment to ensure no shenanigans and that I don't have your information.
Because I want everyone to be able to express their opinion on the question. In order to allow this to be anonymous and not install trackers to keep everyone honest, I am using a trivial donation through a 3rd party to determine you're a real person.
Paying fees and taxes mostly (>65%), but also paying for the web hosting. Servers are not free. The donation is a more upfront monetization approach for the website to be free of trackers, advertisements, cookies, collecting your data and other snooping tricks. You might think other websites are free, but trust me they are getting money from your data and habits or through annoying advertisement. If there is any profit, it will go towards student loans.