Cost is a big part of the reason. A small-ish flan for 6 people costs more than than a "sponge" type cake for 12. And the sponge cake is massive in size compar

Cost is a big part of the reason. A small-ish flan for 6 people costs more than than a "sponge" type cake for 12. And the sponge cake is massive in size comparison because of all the air. And this is why Walmart, for example, will likely never sell proper bread, or other pastry products.