NIMBY stands for "not in my backyard". Somehow people who are sufficiently lucky and affluent to live in a single or double-family house in a nice neighbourhood are expected to welcome the arrival of multi-storey apartment buildings. Otherwise they are despised and browbeaten. NIMBYs, you see, "rarely just come out and admit" that they want to keep living their comfortable lives as they have until now.
The conversation is similar to the one about immigration. People aren't supposed to say that they want the comfort of their communities staying mostly the same as they used to be; that they don't want to be effectively transported to a different country when they leave their home. Or that they don't want to compete with a larger number of contestants for scant resources. This is interpreted as conservative, racist, xenophobic, and otherwise deplorable.