Why is IT strategy hard to define for most folks?

Business is dynamic and IT is the driving force and it is difficult to write or pin down strategy for dynamic system 

One word.. Variable's

An IT Strategy is expected to allow for:
An Agile Business plan
Talent Acquisition 
Cost variation (Global Supply Chain)
Fast paced technology solutions (quickly outdated)
Endpoint growth
Growing Security considerations

Just to name a few, like a colleague used to tell me, "you can't iterate a secure network"

Whilst we're on the topic, anyone else tired of people considering PowerPoint slides a strategy? 

There's no such as thing as "technology strategy" - it should always be the "business and technology strategy" which aka "company strategy". its hard to define because the landscape is always evolving hence the strategy shall adapt to these external forces.

I am of the view that IT strategy should be in line with the business process, if your IT strategy is falling in line with business strategy it is not that hard to lay down and align management. Furthermore, all IT investment should justify ROI to the business, if you're capable of doing so, you're done.

Finding the right amount of stakeholders, but not too many, to allow you a good balance of defining a good roadmap.

You want to make sure you have the key people on-board to gather the feedback of what the needs are. You don't want to make it too many so no decisions are possible.