Why Aung San Suu Kyi is not taking any steps to save Muslims there?
Suu Kyi has a racist instinct against Muslims.
Unfortunately Aung Saan Su Kyi is another Nobel Peace Prize winner who has marked some question marks over "Nobility" of Nobel Prize.
To show you a glimpse of Aung Saan Su Kyi's "impartiality" towards Muslims, she lost her cool last year during an interview by a Muslim BBC presenter and reported to have said the following words off the record:
No one told me I was going to be interviewed by a Muslim 1
Not only her military is responsible for this brutality but she also seems to downplay the reports of human rights violations by her army (Source: Burmese Nobel Prize Winner Aung San Suu Kyi Has Turned Into an Apologist for Genocide Against Muslims) .
Check these excerpts from her official website titled "Fake Rape":
The Information Committee of the State Counsellor’s Office issued a press release concerning the rumours that some women were raped during the area clearance operations of security forces following the violent attacks in Maungtaw Township.
According to the press release, No. 1 Border Guard Police Command Centre (Kyikanpyin), Koetankauk Police Outpost and Ngakhuya Police Outposts were attacked by violent attackers at dawn on 9th October. Nine police officers were killed and a total of 51 assorted weapons and ammunition were lost during the attacks. After the attacks, military columns comprising government troops and the police conducted area clearance operations in the area to recover lost weapons and ammunition and to capture the violent attackers in accordance with the law. However, terrorists fabricated stories with the use of social media and the internet while foreign new agencies spread bad news that was contrary to the ethics of the media by publishing one-sided accusations.
So a short answer of your question, unfortunately, is: 1-) She is biased against Muslims 2-) Everyone from Aung Saan Su Kyi to UN (I personally feel this UN Security Council today's meeting on North Korea is a stagged drama to divert the attention away from Rohingyas)
This was discussed on BBC Radio 4's Today program. Aung San Suu Kyi accepted a constitution in which the Military has a significant role and considerable power. She has no authority over the Military.
It appears that she feels that she must pander to her predominantly Buddhist supporters. She fears that if she were to criticize the Military, it would have no consequence on the ground, and she would lose support. Without a clear majority, she would be sidelined or ousted by the Generals.