It’s not clear why Google wants to do this, but one theory is that it’ll run some workloads more optimally and securely than microdroid.
Microdroid is a "Parallel Virtual Machine". The idea is to offload part of the responsibility of an app to this VM so that it can execute in an environment that is more secure than what Android can guarantee.
So nobody knows why but (in typical Fuchsia fashion) it probably isn't something a consumer would even know or care about.
Honestly at this point fuschia's continued existence feels less like "investing in a product that will yield dividends long-term" and more "middle manager desperately trying to justify their job".
This is going to sound very 'my uncle works for Nintendo' so feel free to not believe me, but the last I heard it was a "talent retention project". Google would rather let some extremely good engineers work on Fuschia, even though it that has very little value, than leave the company and build something higher value for a competitor.