New PS5 model has completely redesigned motherboard - lighter, cooler, uses less power.

[Darth Vader]

I feel like they made a huge thing of the heatsink? Why chsnge it so drastically?

Because they likely didn't have enough data so they went cautious. They didn't want a repeat of the PS4 vacuum cleaner fiasco. Once they got enough data fr various games, countries, etc, they can start downsizing the cooling solution while ensuring it's still whisper quiet.