Read this article, then spend a few days making ice cream, and you'll have a pretty solid grasp on it. I promise, months is an exaggeration.
http://sweets.seriouseats.com/2013/08/how-many-eggs-should-i...
http://sweets.seriouseats.com/2013/08/how-many-eggs-should-i...
If the restaurant is high-end, the icecream should have the correct ingredients to pair with the other food.
Pastry making is often compared to an art... but then art doesn't pay much either.
I do agree with your overall point that chef's skills probably aren't specialized or difficult enough to command high wages in the long term.