Because that's exactly what the landscaping guy did on the phone when I told him.
We'd priced things out online but hadn't yet actually ordered our supplies, so after measuring things out once again (measure twice (or thrice), build once, right?) I phoned a landscaping supply company to place our order.
"I'd like to place an order for some supplies..." I began.
"What is it you're trying to do?" the guy asked.
"Well, we're going to put in some retaining walls..." I began again.
This time the guy on the phone just started laughing.
"Good luck," he (finally) chuckled.
I...didn't know how to respond to that so I think I just sat there in stunned silence.
"It's not that I don't think you can do it," he clarified. "It's just...good luck finding supplies."
Because, turns out, that in addition to the lumber shortage (thanks, COVID), there's also a cement shortage (thanks, COVID). Evidently it's true because this place didn't have supplies for us and every other place I tried didn't have the supplies either.
So now we at least have a good excuse for why our yard will continue to look like a mess for the next few months...