Associating Maya with just ignorance is incomplete.
Maya = Sattva(Goodness) + Rajas(Passion) + Tamas(Ignorance).
Disclaimer: Don't hardcode English meanings of good, passion, ignorance. In real world: A Satvik person can do (so called) bad Karma; A Rajasic person can be ignorant of money/fame; A Tamasic person can be quite knowledgeable.
BG 7.14 — This māyā of Mine,
consisting of the three modes of material nature, is difﬁcult to
overcome. But those who have surrendered unto Me can easily cross
BG 14.5 — Material nature consists of three modes – Sattva(goodness), Rajas(passion) &
Tamas(ignorance). When the eternal living entity comes in contact with
nature, O mighty-armed Arjuna, he becomes conditioned by these modes.
All we experience are proper combinations of Sattva + Rajas + Tamas. When the soul, which is of eternal/forever nature comes into the contact of material nature, it is bound by a body; which is again a certain combination of these 3 modes. This is where the Maya happens for a soul.
Among them Sattva is the purest and closest to the God's manifested form. A person have so many attributes in material life; in certain attributes certain mode will be predominant. Hence we can say that, all the events/Maya around us or by us is projected due to certain combinations of these 3 modes. Hopefully, this knowledge can encourage one to realize that 'I am not the doer of anything'. Since God's spiritual nature is unmanifested to everything else, one has to transcendence beyond all the 3 modes.
BG 14.6 — O sinless one, the
mode of goodness being purest, is illuminating, and it
frees one from all sinful reactions. Those situated in that mode
become conditioned by a sense of happiness and knowledge.
BG 14.10 — Sometimes the mode
of goodness becomes prominent, defeating the modes of passion and
ignorance, O son of Bharata. Sometimes the mode of passion defeats
goodness and ignorance, and at other times ignorance defeats goodness
and passion. In this way there is always competition for supremacy.
BG 3.27 — The spirit soul
bewildered by the inﬂuence of false ego thinks himself the doer of
activities that are in actuality carried out by the three modes of
BG 14.19 — When one properly
sees that in all activities no other performer is at work than these
modes of nature, who is transcendental
to all these modes, he attains My spiritual nature.
who created maya/ignorance?
Samsara/Universe and Maya can be used interchangeably as they represent material world. You may refer multiple answers on this:
How was universe created?
Besides that, Maya can also be described as lack of complete Sattva.
i.e. Maya - Sattva ≠ 0
Until Rajas & Tamas exist, the Maya will exist around the soul.
More precisely, why is it created/exists?
According to famous mystic Jaggi Vasudev (in this video), for any "creation" there cannot be "why". But you want to know exactly that! :-)
From what I explained so far, your question boils down to why Rajas/Tamas got created?
I don't have any definitive answer, except that it's Leela of God. For that, I use an Analogy as below:
Imagine a writer is composing a nice storybook with lot of emotions. Though he is aware that his story is beautiful, he wants to live that story. Using his mystique powers, he sprinkles certain of his subtle bodies into various aspects of the story. His subtle bodies would have attached with certain bold characters, certain weak characters, certain flowers, rivers, trees and so on. Now those subtle bodies are having their own intelligence which they (falsely) assume to be different than their master! Some of them come back to the writer when the chapter is over. But some others become so engrossed that they remain within the characters or elements of that chapter. Writer gets worried and out of compassion, he starts writing chapters after chapters and transferring those subtle bodies to different characters, in a hope that after enjoying various aspects they will come back. After certain time, some of the subtle bodies understand that, they don't belong to the storybook characters but to the author. Hence they again jump out and merge. But certain naughty ones still remain. To get back them, the author also keep sending other powerful & powerless subtle bodies as and when require and the chapters goes on and on...
Here Author is the supreme manifested God, subtle bodies can be souls-demigods-demons-avatars. Storybook is the Maya and chapters are Yugas. The pages & characters can be lives & incarnations.
... if there's any significance of maya/ignorance? ...all Aatman(s)
having ignorance (bounded by karma) and living in the world attain
The significance of Maya is that, it doesn't allow the soul to merge with the God.
Any Atman will get Moksha with a transcendence to all the 3 modes of material life. Not sure if all, because we don't know how many exist.
BG 14.20 — When the embodied
being is able to transcend these three modes associated with the
material body, he can become free from birth, death, old age and their
distresses and can enjoy nectar even in this life.
Because though it appears ideal, the complete existence of Sattva (i.e. lack of Maya) is not possible. No one except supreme God is discounted from the mix of 3 modes.
BG 18.40 — There is no being
existing, either here or among the demigods in the higher planetary
systems, which is freed from these three modes born of material