While that's generally true PowerPoint (and other presentation software that followed in its footstep) not only makes it easy to craft terrible presentations by its default settings it almost guides you along that path the most notorious example being that the default template for any new non-cover slide is the bullet point.

Can you blame inexperienced presentation designers to then fill that blank sheet with as many bullet points as they can?

Inexperienced presentation designers become experienced presentation designers but those habits remain and can be very hard to unlearn, which is how you get expertly crafted 50+ slides monstrosities of bullet-pointy splendour.