Here's why:
* Junk Warrior is a Synchro Monster: It requires a Synchro Summon, which is a specific summoning method that involves combining monsters on the field.
* Synchro Summon Requirements: To Synchro Summon, you need:
* A "Tuner" monster (a monster with the "Tuner" type)
* Non-Tuner monsters with a total Level equal to the Level of the Synchro Monster you want to summon.
* Junk Warrior's Requirements: Junk Warrior requires 1 Tuner monster and 1 or more non-Tuner monsters with a combined Level of 7.
Therefore, you cannot summon Junk Warrior without a Synchro Summon, which inevitably involves a Tuner monster.