But sure, it's all because of Trudeau's ego.
"beginning in early January 2022, DHS will require that all inbound foreign national travelers crossing U.S. land or ferry POEs – whether for essential or non-essential reasons – be fully vaccinated for COVID-19 and provide related proof of vaccination. This approach will provide ample time for essential travelers such as truckers, students, and healthcare workers to get vaccinated."
https://www.dhs.gov/news/2021/10/12/secretary-mayorkas-allow...
So it causes no harmful change for Canadians in general, for as you say, nothing changes.
So... why not give in to this demand then?
As an aside, forcing truckers to get vaccinated makes no sense. They mostly work in isolation, and it isn't like blocking the virus at borders really helps these days.
I support forced vaccination for front line health care workers, those caring for the elderly, where it matters.
Giving in would set a terrible precedent and would undermine Canada's continued existence as a free society.
This allows the federal government to send the army if necessary (although Trudeau said they wouldn't), allows the police to fine and detain protestor that do not want to leave the blockade. And allows the federal government to require private companies to provide services, in this case towing companies to tow the rigs.
It also allows for freezing bank accounts of e.g. companies that have trucks participating in the blockade without a court mandate.
I think, but I am not sure, that this only applies to "strategic sites", in this case the border and maybe highways. Protester blocking a random street in Ottawa may not be concerned.
So, why require the mandate: To prevent the slim minority of truckers participating in the blockade from impacting everyone else for months.