People are already very, very accustomed to thinking in terms of Dollars and Cents. They can easily swap in whole "bitcoin" for "dollar" and "sats" for cents. Giving them symbols that are obvious (a lowercase "b" seems like a "little version" of the uppercase "B" they've seen everywhere) seems like a much friendlier ramp from stuff they're used to than some bizarre tree-looking thing. Bitcoin is weird enough and has enough new concepts as is.