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.
I got it for free with a CPU I bought. Played roughly 3 hours before I stopped. It was just too boring.