The Quest 2 was heavily optimized for reduced cost since otherwise, VR is a very expensive hobby to get into. Before the Quest, you had to buy a $600 headset AND a $1500+ gaming PC if you didn't already have one if you wanted to get into VR.

As it is, I imagine at $300, Facebook is likely losing money on the sale of each headset.

High-end headsets like the Valve Index come with a very good strap. There's no need to mod it or get an aftermarket one because the stock one is already very comfortable and balances the weight on your head very well. But the full kit is $1,000 and requires a gaming PC.