That doesn’t answer the question. WHY do you think it’s more fun to say “my character makes a candle” than “my character buys a candle?” HOW does it enhance a game about killing monsters?
First of all, D&D is, for me, a game about telling stories. Killing monsters is inevitably a part of the stories that D&D generally tells, but it's not the be all and end all. There's LOTS of stuff we'd be hacking out of the game if we decided that killing monsters was all there was. Social skills, for instance.
But even so, taking your candle example, and choosing relatively conventional campaign structures (as opposed to 'the PCs are all running a candlemaking business in their quaint home village', or survival/postapocalyptic stuff where all manufactured/crafted equipment is at a premium)
PCs have rescued a bunch of prisoners from captivity in the underdark and must now find a way to lead them back to the surface. Many of the prisoners are humans and can't see in the dark. There is no wood down here for torches, nobody has spare ruby dust for continual flame, and the light cantrip can only create one light at a time. But a candlemaker might be able to render down monster fat into tallow and make wicks from threads of clothing. Or else, a temple of the god of light has been desecrated by the presence of a now-vanquished Nightwalker, and a PC cleric needs to re-consecrate it. Crafting a single, perfect, holy candle from rare waxes and perfumes, and amid ceremony, lighting it on the broken altar, might do the job. Are you going to wander down to the village and get Gerald the Candlemaker to do that?
Crafting is a story element of the game, one of relatively few which makes it (I'd argue) more precious. It's not to everyone's taste, but hell, D&D-style elemental-themed giants aren't to my taste, and that's never stopped anyone putting them in the game. Let the world-builders and simulationists have SOME bennies, maybe?