I am sorry none of the challengers made the cut. Several people here have pointed out some potential reasons. I'd like to add a few more with suggestions for future campaigns.
The best qualified applicant for any job isn't necessarily the one that gets the job. It boils down to marketing - how one markets oneself on paper and in person. In the case of running for office it also boils down to campaign and marketing strategy -- how to get the word out. As has already been noted this is no easy thing to do with limited funds.
I wonder how many people who were adamant about change made donations to their candidate(s) of choice. It costs money to make signs. Although merely seeing a sign with a name shouldn't be reason enough to vote for someone, there are people who are influenced by these things; minimally, if someone sees quite a bit of support for a challenger that person might be motivated to go research that candidate.
I feel candidates would benefit from campaign teams, not one or two people who guide them. Campaign teams can provide valuable input and feedback on strategy, marketing approaches, and content for written materials and debates. Amongst the four challengers, there were some really good ideas, but a few of the challengers really struggled to make clear points in the two forums I saw and two had trouble putting sentences together. It is critical to have a strategy going in to these debates, with clear prioritized talking points, with knowledge of how to gauge time, with practice in order to make coherent statements, and with the foresight to take time to think before answering questions. (One challenger jumped up to be first to answer a few questions, but jumped up too soon to deliver a thought out response.) Some written content I read contained quite a few grammatical errors, something brought to my attention by several friends before I even had a chance to review the content myself. Should this matter? Maybe not, but people can only judge what they see and hear, and if what they see and hear is fumbling about and error-ridden, it will help formulate an opinion of that candidate. Everything a candidate does, says, and writes is marketing that candidate in some way, but is it effective marketing?
If campaign funds can't cover the cost of mass mailings, candidates could produce handouts/fliers with a summary of their platforms, concerns, and local issues. These should be reviewed and proofed by campaign teams for feedback, with an eye for relevance, succinctness, clarity, accuracy, prioritization, and ease of reading. These could be emailed to supporters to email to their friends. Campaign teams could organize to disseminate this information in various neighborhoods to get the information out there and urge the importance of getting out the vote. Facebook pages could be set up such that this most critical information is always front and center, instead of having to read every post to find issues on the platform.
These are just a few ideas that have been floating around in my head the last several weeks: marketing and strategy. It isn't enough to have a good heart to run for office and serve the community. Heart + marketing + strategy lifts the campaign to a new level, a level that is crucial for success.