That's because it can't invent anything new that it hasn't seen already, and it doesn't understand anything. All it does is remix text that it has come across on the Internet.
( Shhhh!!! You're not supposed to actually say it!)

This is demonstrably not true. Just come up with a description of a ...

This is a first try by GPT-4:

; Input: ASCII character representing a hexadecimal digit in the A register
; Output: Corresponding numeric value in the A register, or $FF if not a valid hex digit

ORA #$20 ; Make sure the input is lowercase (handles both uppercase and lowercase hex digits)
CMP ...

This is the 44 byte C64 entry that assembles to 46 byte executable:

line = 2

* = $304 - (end - next_line)
next_line:
lda #'*'
ldx line
ldy tab_c,x
finish: bmi finish
ldx #12
next_char:
sta $400+24*40+19,y
sta $400+24*40+19-12,x
dex
dey
bpl next_char

jsr $e8ec

inc line
jmp next_line ...

C64, asm, 46 bytes.

Hi folks.

Working on a recent asm project I had the need for a flexible way of printing text strings. All the usual approaches made me impatient, so I put together a macro/function combination that basically makes it possible to use syntax close to C printf()'s. Some examples:

lda #42
sta value ...

sim65 from cc65 package will count cycles when started with -c or --cycles.