Even if the price of on-demand was closer to bulk the economics of it would still be fine.
Buying bulk coretime gives you several benefits over on-demand:
- Unpartitioned bulk coretime can be renewed at a capped price
- With on-demand there is always the risk of prices spiking in case of high-demand
- On-demand chains will at the start only be able to produce a block every 4 relay blocks. link