Why in the Bhagavad Gita does Krishna choose to reveal his true form to Arjuna?

Question

According to Krishna, no one else has ever seen his true form:

To grace you, Arjuna,
I revealed
through self-discipline
my higher form,
which no one but you
has ever beheld -
brilliant, total,
boundless, primal

Not even the gods:

This form you have seen
is rarely revealed;
the gods are constantly craving
for a vision of this form

What could Krishna's reasons be?

Answer 1

It says that Krishna was visible in Rudra Avtar. His size was bigger than Cosmos.

I wonder how he can step on earth having that kind of size.

Answer 2

Krishna chose Arjuna because Arjuna was in a confused stage thinking of his relatives and did not want to fight with them. krishna chose to say the dharma and that is Gita. Moreover, krishna says that he is arjuna in mahabharata.