One explanation would emphasise that the national accounts are showing a picture of the economy which is considerably weaker than that shown by most other indicators. For example, employment growth has been booming throughout the twelve months that GDP has apparently been restrained. The lagging nature of the employment/GDP relationship may explain part of this, but not all of it.
There is a similar discrepancy in the comparison with high business confidence, high consumer confidence, increasing business profits, booming share market and government tax receipts. It would be tempting to disregard the national accounts entirely and rely instead on the other indicators of economic activity mentioned above. However, I do not intend to do so.