Egregoros

@DEERBLOOD they became trendy and soaked up the expendable income of people who got into them. If you want to start a brewery you are losing market share by not making at least one IPA. People who only drink ipas encourage breweries to brew more ipas at the expense of other, perfectly ok varieties. Ipas are the beer of chronic weedoids who are never going to drink anything else and create a local maximum that no force has yet dislodged craft breweries from.
This is rambly but there's a lot of reasons but the tldr is that they are popular with people with expendable income and that keeps craft brewers distracted from doing other things.