Shopping for coffee earlier all the "espresso" coffees seemed to be blends. (??)
I'm speaking from a standpoint of substantial ignorance here, but IMU that's pretty much the norm for espresso.
I think the historic / general standpoint was that espresso was meant to taste like 'espresso.' And, tbf, roast characteristics tend to dominate bean characteristics beyond a certain point (i.e., roast it right dark and it'll taste pretty much the same, no matter what you started out with). And espresso... I believe... was historically thought of as something that needed a dark roast.
A few years back, Hasbean actively advertised themselves (IIRC) as
the pioneers of single origin espresso. Hasbean Steve - I think - posted hither, thither and yon that in order to get a drinkable espresso out of a single origin (SO), you needed a
really exceptional SO bean and a
really enthusiastic roaster. Because if you're e.g. Lavazza and draw on something like 30 beans every year, then irrespective of local weathers / temperaments / crops / yields / conditions you're always going to be able to blast your end product into homogenous and predictable 'dark roast' acceptability. Not least because you're drawing on every coffee producing nation in the world. So something'll always be balanceable, if the end product always contains 30 beans.
But if you're trying to get a drinkable SO espresso from a crop that'll vary year on year, season by season, then you need to spend that much more time working out whether or not a bean is 'balanced' enough (?!) from a particular crop, and what kinda roast it'll benefit from. And what kinda extraction, etc, etc.
And espresso's probably a tonne harder to get out of an SO, because it relies on a 30s high temperature extraction. As opposed to a 4 minute general / waffly infusion with a light roast that'll bring out something interesting from pretty much anything that's put through it.
That's probably all balls, like. But it reflects my general understanding - that SO espresso is harder to produce to an 'acceptable' standard (whilst accepting that 'acceptable' is defined by people's expectations as well as the roaster) with any consistency than a blend, or an SO filter roast.