As with pretty much any staple food. It’s used as a filler. The reason you might not understand is that it can be expensive to eat only meat, veggies, etc. A cheap staple like rice, noodles, or bread is a good way not to die of starvation or at the least keep some money in your pocket.

If a staple food isn’t part of your daily diet, that speaks a bit of privilege on your economic position.

Also I enjoy rice. It’s neutral tasting but with a tiny bit of seasoning it’s good.