Without seeing actual power flow modeling for the lines attached to these data centers no one on the planet can accurately weigh the expense of these customers.
You can't 8760 where and when overloads happen elsewhere, unplanned downtime can't be identified in (or out of) the ISO, you can't forcast demand, you can't plan pre-purchasing of power before it's on demand. You can't speculate on if reconductoring could save money, or remove overloads.
You want to look at rate increases as the core driver. So much so you dump it on replies to others comments. Too many variables are opaque for me to have a discussion about what is the 'largest' factor when each item on the above list could represent 10 million to 8 billion+ in cost.
But I can tell you I won't be convinced that new large loads, and who approved them are not a contributing factor because no one has "proven" it in real time. That's the kind of logical falacy that results in dismissal of real issues.