Because project managers, who invent these things don't want to make themselves redundant.
It's only by pushing the falsehood that the team is so incompetent as to require handholding from someone who likes moving tickets around that they're able to stay in a cushy job.
The interesting thing is: if Agile was invented by software engineers, how come it ended up disfigured in the hands of PMs, reinvented as Agile Coaches? My 2c theory: because the tenets of the Manifesto do not generate interest on the average developer demographics.
The same reason folk religion often focuses on hard, measurable rules (don't work on X, don't eat Y) instead of the more fundamental abstract ones (treat your fellow man as you want him to treat you).