Why do people keep seeing Hachikuji? After stopping not wanting to go home, Araragi Koyomi and Hanekawa Tsubasa keep seeing Hachikuji on the streets. Why does this still keep happening? I thought Hachikuji can only be seen by a person who doesn't want to go home.

Do the effects of the first encounter continue indefinitely, or is this the result of Hachikuji leveling up in the ghost ranks?
As you stated, Hachikuji had one "level UP" as Ghost.

This means she is no more a "Snail", but moreover a "Wandering Spirit".

This means she can generally be seen by anyone having the eyes to see.
Also she no more haunts people not wanting to return home, but strolls about.