If we plan a trip, the destination is often a fixed idea even before thinking about companions.
It's my usual conditional plan: if the destination is clear, like a road trip in Zealand, then I block my dates and budget.
If friends want to join, then we discuss shared expenses and accommodation, but the core of the trip doesn't change.
The influence of friends is just a contingency that adjusts details, not the trigger element of the initial choice.
For example, my annual trip to the Rotterdam jazz festival is always my decision, and friends adapt if they're interested.