I still struggle with why they excluded EU citizens working here from the franchise.
Because it was a referendum for the owners of the country, not the users. People who are citizens. Consider citizenship to be akin to shareholding only shareholders have a say in a company's future, customers do not.
Do non-citizens of Switzerland have voting rights in that country's referenda?
By becoming a citizen an individual is acknowledging a close intimate relationship with a country including a commitment to making its future his or her future. Non-citizens have not made that commitment, hypothetically they always have their own country to return to. Non-British EU citizens can vote in local elections but they do not have any say in the UK's ultimate level of management because they have not made that formal commitment to the UK. If they are withholding their commitment why should they have any say?
I know that PD is rather miffed because some of his colleagues and friends were denied referendum votes. Has he asked them why - after living in this country for many years - they have not taken up citizenship? I dare say their opinions may well have been much closer to mine than to a Brexiter, but if they have not sought to become part of the UK why should they have any say in its future?