Just like parliamentary debating where it is impossible for you to explain how you will solve all problems in a 7-minute speech, real life political campaigns also cannot bring every issue inside society as a “major issue”. What they do instead, is to bring up a specific problem that they want to solve as a party and then tries to promote it as the most important thing to be solved. For example, Labor Party’s slogan in the 2017 UK Election is “for the many, not the few” which signifies that social inequality is the main problem that they want to solve, as opposed to Conservative Party’s “strong and stable leadership” slogan, seeking a solid leadership of UK’s government for future Brexit negotiations.
Failure to choose an issue that is perceived as the most important thing by society is one of the contributing factor to the loss of a certain party in election. For example, in 2016 Scotland Election, Labor Party in Scotland suffers its worst ever loss of votes after it has failed to market itself as either “pro-union” nor “pro-independence” and instead continue campaigning on a platform of social justice, when the thing that is perceived as most important by Scottish then was the problem of Scottish Independence.
Another case study would be the 2017 UK election. Conservative Party also suffers loss of votes after their flagship issue of “strong leadership for a good Brexit deal” is perceived as less important by the British people in comparison to their controversial policy which potentially exacerbates inequality (dementia tax, look it up). Labor Party manages to utilize this momentum and eventually gains its highest vote share since 1945 UK election.
Of course, since this note only takes the two case studies of election, this note does not represent all factors that influence how voters votes for a certain party. Things like patronage (heavy reference to a popular figure as the entire brand of a political party, for example PDP’s branding as “Soekarnois”), attachment to a certain group of people (similar ethnicity, religion, etc.) and many other factors also influences election outcomes.