As someone who worked both as a developer/engineer and as a project manager, the simple answer is a lot of novice (polit word for idiot) PMs choose agile and try to force it on a team just because they heard X famous company applied it or their previous company applied it in some project and worked, but at the end of the day, it is just a tool like any tool you use, it might work in some specific occasion, but definitely it is not the best for everything, and you as a PM who’s getting paid for that specific task, it’s your responsibility to know this, customize it or even create a new approach to achieve the end goal. I have seen and heard so much horror stories of how some PMs are abusing it, or misuse it due to lack of training and knowledge, I remember a friend once said they had a meeting to discuss meetings.. or when some PM try to apply scrum for some niche engineering project with small team where scrum assumes everyone in the team can do the same task, and your engineers have completely different disciplines to start with, list goes on.