Why does reducing public spending have a positive effect on long-term growth?

When we look at the situations of Spain, Portugal and Greece, we see: From 2010 onwards, a sharp reduction in public spending, leading to a fall in real GDP; From 2014 (Spain), 2016 (Portugal) or 2018 (Greece), a recovery in GDP growth that took the level of GDP above the 2008 level in eight years, except in Greece where the level of GDP in early 2024 is still below its 2008 level. We ask the following question: why does cutting public spending boost GDP growth in the long term? The possible answers to this question are that the reduction in public spending: Enables a cut in the tax rate that stimulates demand for goods, supply of goods and labour supply; Leads to a fall in the household savings rate (Ricardian neutrality); Drives down real long-term interest rates and stimulates investment; Leads to a substitut ion of private spending for public spending. The following explanations are apparently in line with the facts: lower tax burden (Spain), lower household savings rate (Greece), lower real interest rates (Spain, Portugal and Greece), substitution of private spending for public spending (Portugal). T he reaction of monetary policy ("whatever it takes") to these countries' difficulties should not be overlooked either .