Five gallons is supposedly the "normal" size batch. What size does everyone actually brew?
It's probably been 12 or 13 years since I brewed a 5 gallon batch, but that was how I started out. The initial equipment I bought didn't allow larger batches unless I did two. I brewed that way for many years always wanting to buy equipment for 10 gallon batches but too cheap to do it. By the time I finally bit the bullet and bought larger format equipment ,I was fairly confident there would never (or rarely) be another failed batch, and it just became an economy of scale.
Years ago I had a lot more traffic through my house and it was hard to keep up given the amount of time I had for brewing. Back then once a month I might have 30 to 40 people at the house for dinner, so that definitely came into play.
I still have large gatherings but they're far less common now because I moved to a place where I'm located more remote. I find myself brewing several weekends in a row and then having months not touching it at all. I may be going back to five gallon batches on stuff I want to experiment with, but I find myself even then, more comfortable just doing the same 10g every time.
The 10 gallon batches can be a double-edged sword. Most of the time I think it's the perfect batch size. But when something doesn't turn out really good to my taste, I find myself
far more likely to dump the beer and just cut my losses. My threshold for what I consider acceptable has raised considerably over the years. I refuse to drink something I don't like and I definitely refuse to serve it to someone else. It's most painful when you purchase two rather expensive kits and then the utility sink drinks then.