Here's why:
* Synchro Summoning Rules: Synchro Summoning requires the total Level of your Synchro Material Monsters to equal the Level of the Synchro Monster you are summoning.
* Maximum Level: The maximum Level for a Synchro Monster is 12.
* Exceeding Levels: Even if you have two monsters that add up to a total Level greater than 12, you still cannot Synchro Summon a Level 12 monster because the maximum Level cap is 12.
Example: You cannot Synchro Summon a Level 12 monster with a Level 8 and a Level 6 monster, even though their total Level is 14.
Important Note: There are some special Synchro Monsters with effects that allow you to bypass the normal Synchro Summoning rules, but these are exceptions to the general rule.