While some minor differences look insignificant, there is a huge conceptual difference between a line not touching another line, or touching it, or crossing it. Or straight/horizontal vs sloped; or smaller vs larger.

Just think about our alphabet:
ijl1r – basically just one vertical line
uv – sloped vs straight
vy – like 人 vs 入 (in “computer” font), or 己 vs 已
wm – like the left part of 比 vs 北, only mirrored vertically
mn – m is like two n’s
pb – which is the longer stroke?
dq – like 土 vs 士
co – closed/touching vs open, similar two 日 vs 曰
hk

And we’ve got only 26 letters, so why can’t they be less similar? Yet most of these pairs look quite different to our eyes. And physics professors love to confuse their students when they use ij and uv for different quantities – in hand-writing on the black board!