The real reason. This should be explained on the site.
Signing up is an extra step, and a little too much, for a product that I want to field test before I decide I want to use it.
I would also second the feedback that requiring an email is undesirable. I know you are doing it so you can count reach and demographics easier and eventually sell those eyeballs or market research. We all need to eat. I get it. However! There is fatigue from needing to log into free services, especially when there are alternatives racing to the bottom with less friction.
You may grow your userbase faster by encouraging early adopters like those who visit this site to use the product. I also believe that the sign-up stopped >50% of the CTRs. I would recommend removing the requirement to sign-up now. Just $0.02 from yet another joe on the internet... :)