What typically incentivizes a professor to change jobs to a lower ranking university?
The most important reasons I can think of are private reasons. People do not live to work, but work to live.
What good does a job at a highly ranked university do, if your family/your friends can not live there or are unhappy to live there? What good does a job at a highly ranked university do, if it is in a place you find boring or don’t like?
I would suggest you to change your mindset from highly ranked university to high quality of life (which is subjective and also includes a little bit the rank of the university, if you value this).
Adding to the family and personal reasons mentioned, I would like to point out some professional reasons as well;
High rank universities tend to be bigger, which means they might be busier, impersonal and more stressful.
A smaller university, (probably of a lower rank), would have a smaller load of students which means the relationship and interaction between professor and students is more direct, more personal and surely fore some, more fun.
Being part of a lower rank institution can be a challenge for the professor to add significant value to it and try to improve its reputation.
And finally yes, there can be tons of other reason such as contributing to a particular local community, living in a smaller and more quiet town, more nature closeby etc. etc.
The question seems to imply that university ranking is the most important component or aspect of a university career. I think many would disagree with that. In fact, there isn't any single feature of academia that is of primary concern to everyone. You can't in general list the various positive and negative aspects of academia on a linear scale that works for anyone but yourself.
Sadly, a lot of questions here seem to make the same sort of assumption. Students want to go to the top university in their country, when it might be better just to want an excellent education.
However, such things as the ranking of a university come with both good and bad aspects. You can brag to your mom, of course, that you are teaching at Harvard or Cambridge. But your life will be pretty hectic and there will be quite a few things that you are expected to do that may not appeal to you. The ranking, of course, is there because everyone is working very hard all the time and take few personal breaks with pressure all the time to do even more. The rankings don't just happen.
So, the title of the question is a bit off. There is no "typical" here, other than perhaps that people desire a change of some sort. But what sort of change is a personal thing. Some want to be a bigger fish in a smaller pond. Some want to take on admin responsibilities not open to them where they are. Some want to move to Montana because of the fishing. Or maybe to Florida.
Your academic career will be a mix of things. Some good and some not so good. If the good outweighs the bad you will probably stick with it. Unless you get a desire for a change.