There was an article in Politico about how they now calculate rankings - there is a thread on it re:UA. You are right though - free tuition and more for an OOS flagship is very appealing! My son stuck with in state as we are in Georgia and he gets free tuition anyway (and didn’t apply for any higher scholarship at UA), and it does attract top quality students.
Interestingly, test scores are now a lower percentage of ranking as they are seen to indicate wealth. Enrolling the highest number of low income students and getting them to graduate seems like a big factor in the rankings. University of Alabama ranking drops to No. 153 in 2020 U.S. News college rankings - what now? - #2 by UA2009