The intuition is that imperfect capital mobility represents only a transitory distortion that delays, but does not hinder the convergence to a long-run equilibrium with higher capital.27 Second, as in the domestic finance and growth literature28, some have argued that nonlinearities play an important role: only if economies have reached a minimum level of  25  See Berka, M., Devereux, M., and C. Engel (2012), “Real Exchange Rate Adjustment in and out of the Eurozone”.
In the first case, let's assume that the economy would have eventually recovered from the shock of the pandemic even without any additional support from unconventional policies. In this case, the economy returns to the pre-pandemic equilibrium (and bond yields), but additional monetary policy stimulus, including the bond purchase program, helps this process to occur much sooner than otherwise.