Surprisingly, she wasn’t lol. Smoke is the most requested, followed by Takeda and rain.
Mileena only seems like she was the most requested because of how toxic her fans are
I see what you are saying, (I couldn't quote the poll you posted for some reason) but I disagree.
These big polls are regularly rigged by people posting on boards etc. I remember a massive poll similar to this saying that Takeda was the biggest character in MKX BEFORE the game came out - I remember being all WTF when it was posted here at the time. The game came out and he was no more popular than any other character. He was even about the 15th most talked about character on TYM in MKXL
Fast forward to MK 11, before the game even came out, and prior to the roster being released, Mileena was amoung the top 6 characters requested in most polls (alongside Scorp/Sub/Kit/Raid/Liu).
After she did not make it, on most polls for DLC from the start she has been number one.
She has been the number #1 trending in gaming a number of times since MK11 came out - Rain, Smoke and Takeda never have- Rain and Mileena came out at the same time and she was higher by a mile. (and made #1 in gaming again)
She is the main one they are advertising - there are special posters of her and she is the most prominent in a lot of the advertising materials etc.
I said before this game even came out, (I posted it numerous times here including before MK 11 was even announced) that Mileena would not be in the initial game and that she would be DLC and NRS would make a shit tonne of money off her. It happened.
I am not saying that the others are not popular, but she is definitely the one #1 most wanted.