This change in the pattern of eruptive activity from large ignimbrites to smaller domes reflects a change in the nature of the magma supply, from large volume flow that heavily interacted with the crust and gave rise to the ignimbrites to smaller volume flows in a colder and thus brittler crust and did not accumulate or interact with it in a significant way.
The change in eruptive activity from large ignimbrites to smaller domes signifies a variation in magma supply nature. It moved from high-volume flows interacting heavily with the crust and generating ignimbrites to lower-volume, cooler flows in a brittle crust that did not significantly accumulate or interact with it.