Because Logic Works Like That.

If you want silly small amounts of gold just because you want to own some gold, get a fanam. It's basically the same thing as a 5 grain bar, except actual old money (not a random made-up bar), and probably cheaper.
A lot of countries made 1/25 ounce, 1 gram, and even 0.5 gram gold bullion as well; those should also be pretty affordable, without being a silly bar. (And then there's the Lady Penrhyn coin of Cook Islands, which at 0.12 grams [about 2 grains] is the smallest modern gold coin ever.)

I'm planning to get a Byzantine tremissis as my first gold ($150), but I might yet find something cheaper. But it won't be a bar.

Nice article NSS!! Thanks!