It has a lot of options, people will answer a few, get bored... scroll down and read some comments.

The options towards the bottom of the list may not get as much attention and votes even if they are used by people.

If it were alphabetical, people might hunt and peck for the one they use most, e.g. PostgreSQL, they might then see things around there (memcached) but fail to scroll back up and vote for Custom too.

Random deals with it well enough without even knowing the poll content or number of options.