They build what they have been asked to build.
So why aren't they asked to build a tyre that actually works Andrew??
What an embarrassment this is turning out to be.
Pirelli are not projecting their road tyre business in the best light imo. 
They've been asked to make tyres that are less durable in an attempt to increase the amount of overtaking. A big part of the problem lies with the lack of in-season testing so Pirelli have to bring tyres that are pretty much prototypes to each race which are then tested in the public eye during each race weekend. Had there still been in-season testing, the tyres could be tested in private with various teams as we used to see with Bridgestone. Drivers having to use both compounds during the race doesn't help things.
I wouldn't say the tyres are a total embarrassment. Yes, I'll agree that it is disappointing to see pitstops by lap 6 and various drivers struggling or not being able to go flat out for the entire race but there are some teams and drivers that are making the tyres work for them. Ultimately, the tyre situation is unlikely to change until the 2014 season (if anyone still watching by then, please let us know) so it'll be a case of the teams and drviers having to learn to work around them.
Hopefully Monaco will be a wet race throughout otherwise there may well be a stupid number of pitstops.