Why exactly is Lori Lightfoot so unpopular?
*gestures at everything that has happened since 2019 in Chicago*But to seriously answer your question: she has done a lot to not just alienate, but also actively antagonize, people since summer 2020. Crime is up, school closures dragged on far too long, she puts her foot in her mouth, and broke a lot of her promises. She also comes off as petty and vindictive, and not capable of managing politics. She also defends herself from criticism with cheap identity politics.
In fairness, some of these things are outside of her control, and she did deliver on a small number of key promises (e.g. 15 dollar minimum wage, civilian police oversight commission, paid down part of the city's pension debt, crime is lower in 2022 than it was in 2020 or 2021 but higher than 2015-2019, etc.). Also, there has been a lot of new investment in the city (I personally noticed how many new industries and businesses have moved to areas in the far south/southeast side like South Deering). She has raised billions to be invested in neglected neighborhoods in the west and south sides. Chicago's credit rating has improved under her. She has both increased and accelerated payments into the pension system, making a small but noticeable dent in the decades-long backlog of payments.
But she isn't good at her primary job of being a leader and administrator; she is instead antagonistic when she doesn't get her way. She doesn't inspire confidence. She engages in a zig-zag type of relationship management with various interest groups (e.g. the business community, progressives, the public sector workers, unions, homeowners, etc.), where one day she will be antagonistic and then the next she'll come crawling back and want to strike a deal, followed again by antagonism. She doesn't seem to acknowledge that the city is in a crisis.
And then there is the fundamental issue of things getting worse under her in terms of schools, crime, and affordability: even if these things are not directly her fault, they happened under her watch and she doesn't seem capable of handling them for another term. Even if you like her and think she has good intentions and is working hard, she doesn't seem effective or capable.
That said, her approval ratings are surprisingly high for how much flak she has gotten:
Maybe it will be enough to save her if all of those 38-40% approvers stick with her in the first round and then the second round opponent isn't appealing. But I wouldn't bet money on that happening.