What came first, the group of roleplayers, or the campaign premise?
The answer varies for each campaign—at least it has in my 15 years’ experience as a game master.
I think there are benefits to deciding up front whether you want to plan your next campaign around the players you expect to have at your table (especially if you have an established group or limited pool of players), or if you want to prioritize your current interests with regards to system, setting, and story premise. Each comes with its own risks and rewards, and it’s up to you what challenges you want to sign up for.
I’ve been sitting at that crossroads for a few weeks now, deciding whether I want to run a campaign that’s more suited to my existing player group’s tastes and interests, or if instead I want to focus on choosing the campaign that I would be most excited to run, knowing there’s a good chance it isn’t what most of the players in my current gaming network would typically want to play.