I think many people quit all kinds of things that are hard. Lots of people receive home brew equipment as a gift, give a try a few times and move on.
I think one reason people quit is home brewing is not easy to get right on the first few batches. Especially if you are used to good quality craft beer. Your first few batches will not compare.Maybe, but who knocks pizza dough or bread out the park first time? Maybe risk/reward is high due to the amount of time.
I do brew to save money. Beer is stupid expensive right now. $6+ bombers, $10+ six packs, $7+ pints. If I factored the time at minimum wage, I'd still be saving on a 10 gallon batch. I think it is unfair to factor time when it is also my hobby. If i wasn't brewing, I'd be out spending or watching tv.
I agree home brewing is cheaper as long as you don't count the value of your time and probably you need to exclude equipment cost. The way I see it equipment and time are costs associated with my hobby. Ingredients, fuel, CO2 are costs associated with the beer.
I always find it funny when people mention the "value of their time" or even equipment costs. Maybe I have gone a bit nuts but I think of brewing beer the same way I look at cooking meals. If you cook dinner at home do you factor in your time shopping, preparing, and cleaning up afterwards? Probably not. If you did you would be eating out all the time.
One of the biggest reasons I brew is because it is dramatically cheaper even when accounting for all the misc. expenses ( propane, cleaning agents, etc.). 5 gallons of your run of the mill craft beer will set you back 80-100 dollars whereas my homebrew is right around 20 dollars for 5 gallons.
I started noticing the decline in homebrewing over a year ago when several of the online forums started to slow way down and/or disappear. There has also been a substantial drop in the number of homebrew clubs in my area and the ones that are still around have less members.
Even this forum is a little dated. There is a sticky on top with results from the 2010 Homebrew Survey?? 6 years really? Look at the Legislative updates. Nothing going on since Spring of 2015?