Why can't core time priced in stable coin?

If technical fellowship is paid(priced) in stable coin and validator may be paid in stable coin (if referendum passes), why can't core time be priced in stable coin as well?

Here is my idea overview:

1. core time priced in stable coin, but when user pays in stable coin, it will be converted to DOT in the backend
2. initial referendum to decide the minimum price of core time (priced in stable coin)
3. The multiplier mechanism can stay the same

What this does:

1. avoid core time being too cheap when DOT price drops
2. create a more predictable spending for parachain teams

Side effect:

1. DOT demand increases if DOT price goes low
2. DOT demand decreases if DOT price goes up