If you start a heavy flywheel spinning the remove the drive. It keeps spinning for a long time.
Inertia is what keeps it spinning even though there is some friction (and drag) slowing it down.
I am not sure you can say that is a correct answer. We humans do not really know why it keeps spinning or why we fly thru the air when a bus stops suddenly.
Inertia describes what we see and experience but we cannot say it happens because of inertia. Newton said it was an innate property of matter but that kind of idea has I think been revised.
We see that when you hit the breaks, you are still pulled forward. That is called inertia.
That is called inertia: the behavior of matter as described by Newton's first law:
An object stays in motion (or at rest) until a force is applied to it.
That is what inertia means: the fact that objects move until you use force to stop them, and don't move until you apply force to move them.
It's like saying something is 'red'. 'red' means an object looks 'red'. It is 'red'. We could use another word for the color, but 'red' is the word we describe for the property of 'being red'.
Inertia is the word we use to describe the property of 'object stays in motion (or rest) unless a force is applied to it'.
Therefor inertia exists because that property exists.
HOW IS THIS EVEN IN DISPUTE?