It’s wild that there is so much space between atoms (and inside them, between the elctron orbitals and the nucleus), and black holes are so incredibly dense, that a small black hole can fall all the way through the Earth and not hit enough matter to gain appreciable mass.
There is a surprising amount of empty space between atoms, and even inside atoms between the electron orbitals and the nucleus. Small black holes are so dense they mostly fall through this empty between-atom space and don’t actually hit anything. Even in a matter-rich environment like inside the Earth, you’d need a black hole with more than half the mass of the moon to be large enough to eat matter faster than it loses matter to Hawking radiation.