Why do you use "towards" not "onto"?

[Ngoc Anh]

English Grammar Tests, Elementary Level

ESL/EFL Test #82 "Prepositons", question 1

I was jogging in the park this morning and saw this dog coming ......... me. It looked like he was going attack me, but he was just trying to reach out for his owner who was running right behind me.

(a) onto
(b) after
(c) towards
(d) below

English Grammar Tests, Elementary Level

ESL/EFL Test #82 "Prepositons", answer 1

I was jogging in the park this morning and saw this dog coming towards me. It looked like he was going attack me, but he was just trying to reach out for his owner who was running right behind me.

Correct answer: (c) towards

Your answer was: incorrect
I was jogging in the park this morning and saw this dog coming onto me. It looked like he was going attack me, but he was just trying to reach out for his owner who was running right behind me.
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WHY DO YOU USE " TOWARDS" NOT "ONTO"?

NGOC ANH

[Mister Micawber]

.
Towards = in the direction of; approaching.
Onto = on top of; to a position on; upon.

The dog is not jumping onto the speaker's body, it is moving in the direction of the speaker.
.
_________________
Canadian-American native speaker
who teaches English for a living at Mister Micawber's
ESL cafe: Interview with Mister Micawber