Why should only people who are fired be allowed to protest? Most of the truckers are vaccinated, but they are protesting for the right of those who aren't to be allowed to do their job.
All of the health and COVID mandate policy is set at the provincial level in Canada, not federally. They should be protesting in Toronto, or other provincial capitals.
However, a good percentage of provincial capitals are currently Conservative governments. So, by deliberatly choosing Ottawa, they're protesting legitimately elected government to force them to step down (despite being democratically elected 6 months ago) and install a new leadership panel made up of the convoy leadership.
They are asking the prime minister to drop the mandates or step down.
I agree that it isn't reasonable to expect the federal government to tell the provinces what to do, but they have been protests in all the major cities as well (so far as I can tell).