the alphabetical order conspiracy might be onto something
I can 100% guarantee you that position in a list is an important factor in which item people pick from that list.
There is certainly evidence to support this, even in US presidential elections. Quotes below from
this article.
"There is a human tendency to lean towards the first name listed on the ballot," says Krosnick, a politics professor at Stanford University. "And that has caused increases on average of about three percentage points for candidates, across lots of races and states and years."
Whilst most people are not affected, it does impact the decisions of people who are unsure who to pick, but also want to (or feel obligated to) vote for
someone. This does make sense. Universal suffrage is a hard-won right, and I can imagine there are people who will make absolutely certain they take advantage of that right, even if they have no real preference of candidate.
In 2016,
"In the states where Trump won very narrowly, his name was also listed first on the ballot in most of those states,"
Also:
In 1996, Bill Clinton received 4% more votes in the regions of California that listed him first in the ballot papers than in those where he featured lower down the list.
Research by Robert Darcy of Oklahoma State University shows that, given the choice, most election officials tend to list their own party's candidates first.
In one famous example of this, Florida's rules meant that Republican governor Jeb Bush's brother George W Bush was placed at the top of the list of candidates in his state, in the 2000 presidential election.
Bush went on to win Florida - which turned out to be a decisive state - by a very narrow margin.
"Because of the fact that different states in the US order candidate names differently and idiosyncratically, and almost none of the states do what Ohio and California do which is to rotate candidate name order across ballots to be fair, we have unfortunately had at least two recent election outcomes that are the result of bias in the name ordering," says Krosnick.
"If all of those states had rotated name order fairly, most likely George W Bush would not have been elected president in 2000, nor would Donald Trump have been elected president in 2016."
Apparently (as of 2017) California and Ohio are the exception:
Some always list parties in the same order. Some allow the state's officials to make a new choice each time. Some put the party that lost in the last election at the top of the ballot. Some list alphabetically.
The "state's officials" bit could be important there - particularly if this is happening in swing states.
Bit of an aside, but presumably (and in fact from personal experience, although not in the US) the effect is more pronounced in committee elections - I have received ballot papers where you can vote for 3 candidates, but there are 10 standing, 5 from each major party. If you just want 3 from your choice of party, but aren't bothered which ones, there's an obvious benefit to being top of the list.