The most functions?
 

If we were to give the championship to the shell with the most functions, you would have a hard time ignoring zsh, that is for sure. However, for routine every day use, Bash (and for that matter tcsh), have so much functionality that only extreme power users even need to resort to zsh. To be blunt, bash, pdksh, zsh, and tcsh have borrowed heavily from one another for the most popular features, and at this stage, though there are differences in their implementations and syntax, each of these shells offers a huge subset of equivalent functionality.

That said, with the way in which bash is set up on virtually all systems, there is no compelling reason to use zsh for most users and bash does an excellent job. Zsh is useful for doing stuff that no other interactive shell does, yet keeping compatibility with the Bourne shell. I get plenty of Bourne Shell compatibility with Bash, therefore I stick with it. I don't want to invest the incremental time to learn how much more I can get out of zsh because I can do so much already with Bash.

winning shell popularity is caused by its own ubiquity
 

Given that bash won by more than 89%, it's highly possible that result is caused by the possibility that bash is the only shell that most people ever used, which is itself caused by the fact that nearly all distributions (in fact, maybe all in total -- certainly all the ones that I know) use bash is the default shell, and sometimes don't even both to install any others in the "default" installation, if such an idea exists (e.g. as in Ubuntu). If this is the truth, as I posit that the popularity of the shell is resultant from its selection by distribution maintainers than fully by user choice (which has been altered [for better or worse] by distribution maintainers), then we can surmise two things: (1) that the poll is meaningless (of course, we knew this anyway, since it's a non-scientific poll) and (2) that people typically only use the shell that is given them, without either finding it necessary or interesting enough to check out the alternatives. It may also be suggested that, in the case that the preceding hypotheses are correct, most of the voters are not shell programmers (who would have both the reasons and the skills to use alternative shells, at least for sport if not for work, etc.) but just normal users who may even stay away from the command line altogether for most tasks, and voted only in passing selecting the only option with which they were familiar and had heard something about -- the ubiquitous Linux shell, bash.

"Bourne again" or "born again"
what so ever love bash