Well, it appears that there is no reason other than Brits love being stubborn and are suckers for tradition.
Some research from the BBC revealed that there isn't a set rule that elections should be held on a Thursday. But it has been that way since 1931 and, with this being the United Kingdom, no one has thought to challenge it.
However, there is a slightly more logical reason, albeit theories, as to why this rule was implemented all those decades ago.
Apparently Fridays were considered to be too risky as they were a payday and it was presumed that everyone would go to the pub instead.
Not an awful alternative, given the options.
Sunday's were also ruled out as there were fears that priests' sermons would influence voters decisions.
Thursdays were seen as a safe bet - they were usually market days and people would be travelling to town anyway, which was convenient.
The 2011 Fixed-Term Parliament act did introduce a law where an election must be held on the first Thursday in May every five years, apart from exceptions, such as this year and 2017, which were held in December and June respectively.