In Latin-descended languages, ille became both the definite article and the third-person pronoun.
Why didn't ipse and hic also degenerate into adjective-like or enclitic forms?
It's hard to imagine how such forms would feel or function.
Trying a couple of examples:
Ipse hair needs a trim = Hair right here, on me, needs cutting.
Hic house needs painting = House familiar to you needs painting.
Aha! They perform pretty much the same function as possessives, which may explain why they weren't needed.
Ipse hair = My hair, Hic house = Your house.
There's a semantic distinction, but it's weak. Weak distinctions always fade out.
From another angle: Though ipse hair and hic house never came into use, they do show up as missing places in a table. Try applying the to both situations.
The hair needs a trim = NOT my hair, somebody else's hair.
The house needs painting = NOT your house, some other house.
Ille retains its over-yonder feel and doesn't work well in ipse or hic situations.
= = = = =
Later and MUCH simpler answer: We don't need ipse and hic forms as articles because we have this and that. This = ipse, that = hic, the = ille. We call this/that demonstrative pronouns instead of articles, but all three are strictly parallel.
This little exercise wasn't entirely pointless. It helped to display a normally hidden pattern in grammar, and helped to refine the semantics of a common word.
The current icon shows Polistra using a Personal Equation Machine.