The radial layout of memories is primarily to ease PCB routing. The data/clock lines going to each memory chip need to be equidistant which is much easier when the chips are equidistant. The GDDR6 memories are relatively far from the CPU which may be for cooling.
Lots of laptop makers manage this with a much smaller PCB.
I'd guess simply not much effort went into making the PCB small and cheap.
I would guess there will be a follow-up revision of the PS5 with all hardware much cheaper. That model will be the mass market one, and the profit maker for Sony.
