In my experience of running hosting business people want to pay month to month or yearly. I think we maybe had two or three customers that wanted to pay biannually, not worth the bother.
We had large upfront costs (servers) and lots of competition so low margins. If the customer was paying month to month usually they would stay long enough for us to easily manage the server and keep it profitable.
But some packages had more customer churn, You will pay for you backup hosting no matter what but a cheap server for an experiment is not going to see enough months to be profitable.
Making these high customer churn products a yearly thing made them profitable. Similar thinking for products that are just dirt cheap, add in the cc fees and other costs of billing, if its late or declined, it makes much more sense and profit to charge £24 a year for an email than £2 a month.