Small parties also provide a protest vote, and since voting occurs on a riding-by-riding basis, the desire and intent of the protest can vary. Sometimes protests can be so widespread that no government can form a majority. In Canada, we managed to elect three minority governments in a row over a period of seven years (2004 - 2011).
In short, voters use small parties to send a message.
[0] The NDP's first national leader, Tommy Douglas, was never Prime Minister, but is known as "father of Medicare" and is generally well regarded by Canadians decades after his death.
For example, at least a part of current Brexit hassle is because the DUP (with their 1.5% of total MP seats) are needed by May's government, and they got to veto one of possible options of solving the Ireland-North Ireland customs border issue. There are many other examples worldwide, where small parties focused on a particular domain of problems can get an oversized influence in that domain.
In some other systems, you can choose multiple options. This makes it possible to represent an opinion like "Starbucks CEO, then Democrats, then Libertarians, then Republicans", and so smaller parties can still get votes without compromising the election of larger aligned parties.
They should be able to give there "dropped" votes to a bigger party for a legislative period, for negotiated terms.
"If you promise to push opticfibre to all homes in these citys, you can have our voters voice for the next 4 years."
This would solve the problem of unheard voices and- allow actual negotiating politicians to be trained and get busy.
Take the Green Party in Canada. Without it, the remaining left(ish) parties in Canada only have to go a little better than the Conservatives on the environment to get the environmental vote. With the Greens in, they have to at least meet them half-way or they risk further splitting the centre-left.
They also sometimes hold the balance of power. This puts their issue front and centre.
The right doesnt oppose clean air, it opposes giving Al Gore's carbon credit company a blank check.
The right (in the US) could just as easily ask why has boarder security become a left right issue.
That's because the right made it a partisan issue.
https://www.fairus.org/issue/legal-immigration/us-commission... The bipartisan Jordan Commission recommended cutting legal immigration in half and punishing employers for hirin illegals. The democrats made this a partisan issue.