Why do brewers not list IBUs?

As a professional I just wanted to add two points to this. Number one, calculations are just that until the beer is tested on a photospectrometer to confirm it. Most small brewers don't have a photospectrometer, and don't get their beers tested, so they don't know how close their calculations are to what's actually being produced. Two, due to process variations calculations can be way off, particularly in breweries where multiple people are brewing. What I'm talking about are the basics: Is the beer at the specified gravity? Have the hops been properly weighed? How were they stored? How old are they? When exactly were they added to the boil? How long is the spin segment of the whirlpool, and how long is the rest? How long does the knockout take? What's the temperature of the wort during knockout? There are variables in all of these things that can change the final measurement.

 

UBUs became a "thing" at the end of the last century as west coast IPAs were asserting their dominance. I still have my RRBC Pliny the Elder 100 IBU T-shirt that brags about it. But now, not so much. It's just one of many details about a brew.

Barebottle in San Francisco puts their recipe and stats on every can.