They do so because much of the media repeatedly report those promises uncritically. in doing so they give those unicorns false legitimacy.
It's not the same thing. That only works when people AREN'T being deliberately disingenuous, which is the case here.
Make them explain, in detail HOW they will deliver stuff. If they can't don't report the promise. Just say they brought an unrealistic idea to the table.
It's the HEIGHT of journalistic delusion not to accept that.
To fight lies you deny them air not print them uncritically. That's crap reporting, nowt else.