Regardless of the original reason, it keeps drips from running down the neck all the way to the bottom, which can stain surfaces with surprising tenacity.

According to the company, according to legend, after the founder's death, his two sons took over the business. They wanted to rebrand the bottle to enter the bitters into competitions. One redesigned the bottle, the other redesigned the label.
It was either too late to fix the mistake or they were too stubborn. One judge advised them to keep it, since it would be eye-catching for customers. They kept the glitch.

I'll often order a "soda and bitters" (carbonated water with a few dashes of this) when I'm out with friends but don't want to pound alcohol. It looks like a cocktail (so folks don't ask why I'm not drinking), keeps me hydrated, gives me something to do with my hands, and tastes like Christmas. Highly recommend.

Aren't most bitters 30-40%? Have to check my collection of various bitters when I get home. I know for sure that actual vanilla extract is usually 15%+

Edit: also it's always bothered me the angostura has the label go so far above the start of the bottle's neck

1 measure heavily smoked mezcal
½ measure of gin
½ measure of demerara rum
5 heavy dashes of angostura bitters
Juice of 1 half lime Top with carbonated water and express lime rind on the result

I call it Pink Smoke