You may won't like it but I can't agree with you on this opinion of
'Bangladeshi Applicants"!
Visa officer doesn't look for who is Bangladeshi applicant and who is Australian applicant to judge whether they will conduct an interview or not. It depends on the cases, application structure, red flags, divorce and so many other factors.
I completely understand your and situation/frustration and I can only imagine since 5.5 months was like ages for me. But the truth is you really know why they put you on interview queue better than anyone else and you also know that it may make sense (Based on if you put yourself on V Officer's shoe).
If country of origin is the only facts, then please go to Nairobi/NDVO (For some Afghan applicants) thread and see how fast some applicants processed because of solid and straight forward cases.
And also visit Australia/USA/London/Vienna pages to see some waiting for long time and some are in interview queue.
Someone please correct me, if I am wrong.
I wish all of us fast processing and good news soon.