It is (or should be) part of the dictionary definition of each verb (and many adjectives and nouns) what kinds of object or complement they take.

It happens that

Hear takes a direction object: "I heard him"

but

Listen requires a "to" object: "I listened to him".

Similarly

See takes a direct object: "Did you see the show?"

and

Watch takes a direct object; "Did you watch the show?"

but

Look does not, and requires an "at" object: "Did you look at the book?"

There's no rule or logic to this: it's just the way English happens to work at this stage in its history.

It is (or should be) part of the dictionary definition of each verb (and many adjectives and nouns) what kinds of object or complement they take.

It happens that hear takes a direction object:

I heard him.

but listen requires a "to" object:

I listened to him.

Similarly, see takes a direct object:

Did you see the show?

and watch also takes a direct object:

Did you watch the show?

but look does not, and requires an "at" object:

Did you look at the book?

There's no rule or logic to this: it's just the way English happens to work at this stage in its history.