Based on various non-anime sources and the precedent shown in earlier episodes / followed in later episodes, there seems to have been a requirement on Kunai with Chain that it could only be used by Warrior and Beast-Warrior monsters.
While this wasn't written into the text of the card in the show, the theory does fit with the basic premise that Duelist Kingdom era Yu-Gi-Oh! that "It has to be somewhat reasonable within the 'lore' of the game." As a relatively generic "weapon", its use would thus be limited to Warriors ("trained" in the use of weapons).
Supporting the implicit/explicit "Warrior or Beast-Warrior only" clause:
In earlier episodes (https://yugipedia.com/wiki/Kunai_with_Chain_(anime)):
- Episode 19: In the duel with the Paradox Brothers, Axe Raider (Warrior) and Celtic Guardian (Warrior) receive the effects.
- Episode 31: In the duel with Bandit Keith, Garoozis (Beast-Warrior) receives the effect.
- Episode 34: In the duel with Yugi, the effect is again demonstrated as being used by Garoozis (Beast-Warrior)
In later episodes, post-Duelist Kingdom:
- Episode 44: The original "Virtual World", used by Axe Raider (Warrior) (not technically a "duel" since this is the original RPG-like game being beta'd by Kaiba Corp)
- Episode 69: In the duel with Mako Tsunami in Battle City, used by Panther Warrior (Beast-Warrior)
- Episode 111: In the tag duel with Yugi vs "The Big Five" in the full "Virtual World" arc, used by Alligator's Sword (Beast-Warrior)
All of these instances are consistent with the idea that Kunai with Chain must be used by a Warrior or Beast-Warrior monster.
In non-anime sources, when Kunai with Chain is used directly as a power-up spell (and not as a trap consistent with it's real-life version), it usually includes the requirement for Warrior and Beast-Warrior monsters. Examples include:
- Various games describe the Kunai with Chain "spell" card as "featuring the effects of... the Legendary Sword and the Sword of Ruin." Each of these spells existing separately in those games and referring to "drawing out the power of Warriors." EX: Dark Duel Stories, Forbidden Memories
- The game Duelist of the Roses has the effect "Increases the power of WARRIOR and BEAST-WARRIOR monsters by 500 points"
- The games The Sacred Cards and Reshef of Destruction both specify "It can be equipped by any warrior..."
Notably, all of those examples are in versions of the game that either are not based on the traditional Duel Monsters format or are heavily adapted from the real-life format because of technical limitations.
Between all of these examples seeming to indicate intent to be Warrior or Beast-Warriors only and the tendency for Duelist Kingdom era Yu-Gi-Oh! to be incredibly inconsistent with what cards do, this is one of the cases where the show was relatively consistent about this restriction.