Says The Economist. The authors argue that falling state capacity, incompetence, corruption, and transfer/entitlement spending, which crowds out public investment and services, are to blame.

Update: Related, in VoxEU, Martin Larch and Wouter van der Wielen argue that

[g]overnments lamenting a stifling effect of fiscal rules on public investment are often those that have a poor compliance record and, as a result, high debt. They tend to deviate from rules not to increase public investment but to raise other expenditure items.