Here's why:
* Trap Hole is a Normal Trap Card.
* Normal Trap Cards can be activated during your opponent's Main Phase 1 or 2, as long as the card's activation conditions are met.
* Trap Hole's activation condition is simply that a monster is Special Summoned.
* Synchro Summoning is a form of Special Summon.
Therefore, if you Synchro Summon a monster, your opponent can activate Trap Hole during their next Main Phase.
However, it's important to note:
* If your Synchro Summon is performed during your opponent's turn, they can activate Trap Hole immediately after you complete the Synchro Summon.
* If you Synchro Summon during your own turn, your opponent can activate Trap Hole during their next Main Phase.
Keep in mind: Trap Hole only targets monsters that are Special Summoned, not monsters that are Normal Summoned or Flip Summoned.