Exactly. Before I as a DM start a campaign, I make sure everyone knows what it'll be about.Oh, and Conductor? You should always let the passengers know where your train is going before you start selling tickets.
For my current campaign I wrote a short overview, describing setting, people, and theme. I described recent events, hinted at things to come and defined their proposed role.
I also made a list of 'houserules' I wanted to use and provided a list of allowed races.
After collecting initial feedback I made some minimal adjustments, and off we went!
We're now into our 6th year and I haven't had any problems with 'station squatting'. So far there's only one character that can be hard to convince to engage in 'adventuring' from time to time.
Over time I've also loosened some of the initial restrictions to allow for a wider range of character concepts.
Then again, I've known most of my players for about two decades, so I know what playstyle they enjoy...