Voters in Ohio went to the polls to decide whether to approve a measure known as Issue 1 that would raise the bar for constitutional amendments on the ballot. In the ultimate irony, the votes against changing the amendment process exceeded the 60% supermajority that the measure was seeking in the first place
The easiest answer is because this was a special election in the middle of August with just one item on the ballot, which is exactly why the GOP broke their own new rule eliminating special elections in August, because they were hoping voter apathy would push them over the finish line. I’m very happy, and slightly surprised that they ended up being wrong, but I don’t think they’ll take any kind of lesson from this.