They're priced as they are because it's a pain in the ass to go out and get Amethyst and Garnet gems when you could be out mining valuable gold at Halatali. This increases their value. The supply of those gems in the wards is lower than the other T2 gems so they tend to be priced higher when they are on sale, this means people aren't likely to skill up on them.
If we used the kind of logic you're using then all NQ items would cost less than the total cost of materials. Problem is items reach a value where no one bothers to make them because they aren't worth the bazaar space or the effort of synthing it. For Garnet and Amethyst rings I place this at 50. If the price drops below that I stop making and move on to something better. If the price drops lower then others stop making them and you end up with none up for sale.
Ok your lance. What if people come along and list those four at 100k? You have to go even lower which means you're getting at least 70k less than you could have. Then they go lower than you again etc. You're better off NPCing it if you don't care about the gil to save yourself the trouble. Back when we had that undercutting issue with electrum ring +1s I ended up giving them to LS members because it wasn't worth the effort any more.