Stress
The majority of glassblowers set their own hours, which is pretty liberating. But the difference between setting your own hours and living life stress-free is pretty huge. A lot of glassblowers are really just hobbyists, working menial day jobs in order to support this (blow)pipedream. It's only stressful if you're late to the craft fair you promised you'd show up for.
As for the glassblowers who make a full career out of this? They spend their lives working long, tiring hours in the backroom of a forgotten glass studio, desperately hoping for a customer (any customer) to walk in. It can be fairly stressful when there are a lot of orders, but much more stressful if there aren't any orders to be had. You might be able to blow glass, but you certainly shouldn't eat it.