Did those come in a set? Or did you have to buy them separately? That is pretty weird, those are pretty standardized for the most part. I think mine were on the short side, about 2.25" overall (Husky brand), Craftsman, Proto, Allen, and old MAC sockets were not much longer. NGK/Denso plugs are generally about 5cm from the seat to the top of the plug ~ 1.9" - so those sparkplug sockets were just barely long enough.
I'd double check that the plug really is too long for the socket - test it with the new plugs. Then double check that there is nothing inside the spark plug tube. Somethings that rubber tip on the coil on plug igniter can come loose and lodge inside the tube.
Corrosion or physical obstructions are other possibilities - I've run into this a couple of times on other applications. Worked on a small block Chevy - 7 plugs came out no problem, last plug couldn't get grabbed by the socket.
Possible that you got a weird setup of sparkplug socket - maybe they took a regular thin wall, deep socket and turned it into a sparkplug socket. As far I remember, all my sparkplug sockets have the insert (rubber or magnetic) and were engraved or otherwise marked as for sparkplugs exclusively.