Kitchen cupboards

The oldest of my kitchen cupboards is a little over 6 years old, as I put it in when we moved in. (There are older ones, but they were already there.)
The thing that makes we wonder is, why when they take a lot of trouble for the cupboards to fit together, and be strong, do they then put tiny plastic supports to hold the shelves up? These are kitchen cupboards. A plate, cup, tin of beans, bag of flour may not be that heavy individually, yet when you have a normal amount in the cupboard, their combined weight is heavy, and the tiny plastic shelf support gives way. Why can't they make metal shelf supports, or a piece of timber under the shelf to support it?
I think they expect people to renew their kitchen, but why should you, when all that is wrong is the shelf support is inferior to the rest of the product?
The reason for this question arising with me is that the ones holding up the shelf under my sink have given way.
"Perhaps she has a huge weight on them,"" I hear you say, but you would be wrong. The shelf has my iron on it, and then plastic storage boxes, empty spare ones! So the weight on the shelf is minimal. When I'm fit and well again, that will have to be one of my priorities, fixing that shelf, and strengthening the supports on all the other shelves.