The reason for extremism gaining traction is relatively known, but OP was questioning the more subtle “conservative”-leaning parties being in power globally (seemingly) for the past decade at least. That’s somewhat harder to explain. For example, it’s harder to explain how most western countries became neo-liberal at the end of the 90s.
Extremism gains traction when there’s societal divide with at least one of the divisions significantly poorer than the other.