FT’s David Pilling asks this question in a great piece interrogating Madagascar’s decline:

President Hery Rajaonarimampianina is weathering the latest in a series of political crises that have debilitated his nation since independence in 1960. In that period, Madagascar is the world’s only non-conflict country to have become poorer, according to the World Bank. Its income per head has nearly halved, to about $400 [see image with the sobering trend data from the World Bank].

A leading candidate for explaining the decline is that the Malagasy state does very little:

“Madagascar is the world’s forgotten island,” said Patrick Imam, the IMF’s representative to the country, who argues the west should pay more attention. “This is probably one of the few countries in the world where the IMF cautions the government: ‘You are not spending enough money,’” he says, referring to the limited presence of the state outside Antananarivo.

According to World Bank data, since the mid-1960s government expenditure in Madagascar has consistently been below the regional average:

Read the whole thing here.

A somewhat speculative explanation might be the abolition of the Merina monarchy in the late 19th century by the French. For much of its post-colonial history Madagascar has been racked by one episode of elite political instability after another. A stable monarchy might have provided a nucleus around which to construct elite consensus on legitimate means of organizing the country’s political economy.