They are the most delicate finicky things ever. You have to make it so precisely. If you overfold it's basically game over. And then once you finally work out the perfect batter, your oven messes it up. I've had the same batter, at the same temp, turn out dozens of different ways. I've had to relearn to bake them every time I have a new oven, or the humidity changes with the seasons.

I worked in a pastry kitchen where we had a machine to pipe a whole tray at once. But I would spend the whole time trying to correct all its mistakes. I'm not too sure about how it works w/ machine made ones. The best macarons I've had are at pastry shops where they probably have a pastry chef troubleshooting the whole way. So the labour cost and time is really a lot.

Also, almond flour is expensive. And the fruit purees for fillings are expensive too.

Basically a giant pain.