That's a bit of a poor travel agent who has just given up because a flight is not on their favourite booking engine.
In my experience of connecting onto the minor Finnish domestic operations (in my case going to Lappeenranta when Golden Air and then others ran the route from Helsinki) they are fine with people changing to the flight before/after, and not the approach of supposedly more "developed" aviation markets where, if you miss a connection, not only do you need to buy another ticket but at four times what you originally paid.
Given that commercial services to Pori (again a bit like Lappeenranta) have been started and lost again a few times in recent years, flights are unlikely to be full.
If you want to be sure you can always email them and ask.