10% interest rate => "why invest in this new factory for a 10% return when I can just keep money in the bank?"
0% interest rate => "well if I want to make money, I need to invest"
Feel free to blame other things - maybe 0% inflation rate (higher inflation => more opportunity cost of not investing) or QE (which is similar to 0% interest rates, but still different - a 0% interest rate environment persists since early 2000s whereas QE only started after 2009) which is much more problematic as it floods the market (but not the economy) with money and pushes equity prices through the roof (despite shitty fundamentals).
0% interest rate -> I'll take my money and leave for greener pastures (other countries such as emerging markets).
Western central banks can't raise interest rates above the lower bound without triggering unacceptable unemployment or even deflation. Indeed, the highest safe rate has fallen in the wake of every recession.
To me, this suggests major structural problems in the western economies. It's hard to think of a single explanation that applies to all (pre-pandemic) zero-interest rate western economies, however. The economic foundations in Australia, Canada, the UK, the US, and the EU are different enough that there is no obvious single structural fault common to all of them.
There is one though: changing demographics - the median age of the population is going up and the percentage of the working population is going down.
The Western world has been relatively stagnant in this regard for two generations already.
https://tradingeconomics.com/united-states/interest-rate
If investment (real investment, based on profit) is not worth it, and only the central bank wants a piece of the overpriced action, then we have essentially a centralized economy. This breeds stagnation.
Contrast to China, who had healthier yields, and only lowered them for COVID: https://tradingeconomics.com/china/interest-rate