Opaque is great and many times a bit smoother to print on.
Our local suppliers sell 1,000 precut 18" x 24" to 1 opaque of the same size. So they rarely have any. Like everyone, storage space and inventory costs concern them. They say there is little call for those blanks.
When you compete it does no good to tell a political org. how much better the opaque is going to be when pennies per unit count, especially when the life term of use is very short, as all they want is CHEAP!!!
Guys who plaster neighborhoods with snipe signs do not want to pay the price difference either as they know code enforcement may only be hours behind them in picking them up.
So who is left who uses small coro signs? Real estate agents and builders. And those folks aren't spending if they are still in business.
No that I disagree with using opaque. I prefer it. Customers, in the main, don't when price is the only consideration.