Well, TGD has clearly stated previously: "You will understand why we did things this way, once we are finished."
TGD is in the process of amassing mountains of data and biomarkers with which to convince the FDA that both A-273 and 3-71 are efficacious and safe across multiple neurodegenerative and neurodevelopmental diseases.
I'm guessing that TGD's strategy, although taking longer, is designed to minimize overlaps in trials across multiple neurodegenerative and neurodevelopmental diseases.