In my nearly 5 years at Illinois, I know of only two transfers out of somewhere around 800 students between 2019 and 2024. Both were island students. One joined the class of 2020, but had to repeat the entirety of her first year. The other joined the class of 2023 this year as a second year. Not going to lie, it is unlikely there's another transfer in our midst that the few of us on here from Illinois don't know about.
I would not bank on a transfer into Illinois. Our curriculum is hard to line up with other schools, though obviously at least 1 has made it work recently. This becomes especially true the further into the curriculum you get. If you don't come in between 1st and 2nd year, definitely do not have high hopes of coming in between 2nd and 3rd year. We have a pretty stable class composition with very few people dropping from class to class or leaving outright. Tack on that the school strives to maintain a 130 class number very stringently (within reason of course; my class is 133). So if a class doesn't lose anyone, the chances of a transfer for any reason goes down, regardless of if it is "compelling". Then you really need to have a compelling reason to transfer in. Wanting increased exposure to wildlife species will not be a compelling reason. A large proportion of each class expresses a desire to go into zoo med/exotics/wildlife, and if it was a compelling reason for transfer, there'd be literal dozens of applications per year I would imagine. The fact that you're in state is a much better reason, but you would have to convince the admissions committee why you deserve a transfer when an Illinois resident going to, say CSU, doesn't, ya know?
If you would like pros/cons lists, there's definitely a ton of information in the "x vs y" schools threads that include information from several of us regulars as well as others who don't regularly post here any more. There's definitely several posts that outline grievances that people have in those threads, which I think are important for people to look at. Us regular posters have had an overall more positive experience than those posters, so have a more biased view towards Illinois. You're welcome to PM too.