I suppose because the EU specified this as an issue. Since they have set this as an issue it is not unreasonable for them to come out with proposed solutions; this does not mean the UK should not actively play a role, but it does mean that the EU approach of saying this is a red line for us but we are not going to think about how to address this issue, just say NO with whatever the UK suggests is not the best approach to achieving a practical solution.
The EU could be pro-active.
The Good Friday Agreement is pretty important. It directly affects the UK and an EU member state that the EU is not going to abandon.
May has accepted the importance of the GFA. She is now rejecting the backstop that she previously agreed to that would protect the GFA by ensuring the Irish Border remains open.
To be fair to her, she did provide her own proposal. Unfortunately, it was utterly unworkable. She might find the EU backstop politically unpalatable, but at least it is logically possible. Hers requires magic. And even proponents of the scheme accept that the infrastructure isn't in place and won't be by the time we leave the EU.
So no, I don't blame the EU for rejecting something that wouldn't work.