> nothing on it is designed as an attachment point
I would be curious to know why they didn't implemented anything like this. I know that no robot, space vehicle or any other technology currently exists that could repair such a spacecraft in L2, but I would like to know whether leaving this door open by adding one or more attachment points would have increased the cost of the telescope too much.
Mass and volume are at a premium on any satellite. Adding attachment points and access panels would have reduced the capacity for scientific instruments. Since NASA has no repair capacity now or even seriously planned for the future, it was pointless to design for serviceability. Building and launching a whole replacement JWST would certainly be cheaper, considering that they have some experience now.
I would be curious to know why they didn't implemented anything like this. I know that no robot, space vehicle or any other technology currently exists that could repair such a spacecraft in L2, but I would like to know whether leaving this door open by adding one or more attachment points would have increased the cost of the telescope too much.