Politicians think it's a moonshot project at finding another nuclear bomb type of thing. (None of this would ever be funded without the tenuous nuclear weapons connection.)
I'm intimately familiar with how high-energy physicists get hired and funded. The funding comes from the political and budget bucket labeled "nuke stuff".
E.g., Fermilab is under the U.S. Department of Energy. CERN is funded by the European Organization for Nuclear Research. Etc., etc.
Politicians fund this stuff only because it triggers their wunderwaffen FOMO.
I think only surpassed by the SETI program in terms of doing it because many nerds think it's really cool.