Anton here :
This was fundamentally brought on by a lack of good other places to put your money, due to a sustained commercial crisis combining a trading depression in the Mediterranean and a fall in interest rates (down to 0.25% pa in Florence).
The period also saw a 'culture war' between the Humanists and the Scholastics, and as the Humanists concentrated on winning the argument rather than having their facts and logic straight, they successfully painted the 'moderns' (ie the Scholastics) as backward relics of the dark medieval era and the Humanists therefore got all the cool jobs as Court Poets, Historians and so on.
The combination of the physical evidence of the changes in fashion evident in the new art, styles of houses and so on, combined with the documentary "evidence" of the polemics of the Humanists caused it to be mistaken for an intermediate period between the medieval and modern worlds by nineteenth century historians (especially Burkhardt). Medievalists are still trying to repair the damage.