I'll bet it's the lack of sun....hostas are shade tolerant ( as ken is so fond of saying) not shade loving.

As a matter of fact, nothing seems to grow in that area under the pyracantha

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i think you answered your own question ... MOVE THEM .. or they will all disappear ...

i am guessing, but i wouldnt be surprised if you are barely able to put a shovel through the roots ... ergo.. they are starved for water.. the plant taking it all before the hosta can benefit ...

under a norway maple.. grass cant even grow... the most invasive weed in the world ... you are suggesting the same under this plant ..

if you can grow nothing under a given plant... it is because that plant is to aggressive ...

ken

Lack of bright light and tree roots are the likely culprits. I'd move the hostas. When you go to dig one up you will probably see the heavy root competition to confirm that part.

-Babka