Ixixly,
Having ground crew to shepherd the pax means...you must have ground crew in place. I fly charter and corporate flights that, at the moment, can go anywhere withiin the US and can be on little to no notice. Soon that will include the whole of the Caribbean. I used to do similar in Australia. It's not practicable to employ someone at every airfield in the US just in case we should stop by. If we carry someone then that's at least one fewer pax, less baggage &/or shorter range.
'Power by the Hour' & similar schemes doesn't necessarily reduce the hourly operating cost, except for nasty surprises. You're effectively paying for someone else to take the risk and they want their profit margin on top of that cost. Insurance is never free or cheap, just cheaper than a calamity you can't afford to risk.
Many jurisdictions prohibit or severely restrict single engine ops compared to multi. Try doing flights overwater, or at night, or IFR in various countries and the op. is only practicable in a twin. Shetland, for example, is an area where a PAC750XL would be great - short(!) strips, short hops, limited number of sectors per day - but the overwater nature, and need to resort to IFR when the weather closes in, makes it not possible under . In the US, single engine is OK for IFR charter but then you have weather & overwater limitations that don't apply to twins.