Consumer behaviour

What countries? What time period? If you are referring to the USA, it has to do with Keynesian demand-side economics. This theory believes the economy is driven by spending (whether frivolous spending or not). The Federal Reserve lowers the interest rates which encourages people to borrow and spend instead of saving. This has been going on for 6 years now. Many other countries followed the lead of the USA doing the same and organizations like IMF push the same nonsense.