Let's say I have a 70% chance to Persuade someone.
If you put in a single persuasion check in a conversation I will succeed on a roll of 7 or better.
If you add in a second Persuade check in the same conversation I now only have a 49% chance of succeeding.
Adding in a 3rd Persuade check means I only have a 35% chance.
The dice are fickle enough as it is, having multiple checks per conversation makes failure likely and players frustrated.
