To some extent true. However... look at the Republic of Ireland, population just over 4,7 million (versus 2,7 million within the smallish triangle of Helsinki - Turku - Tampere area, roughly Ireland size). In ROI substantially more p2p flights exist, dozens of times more, not only to warm destinations.
Another reason? Most of Finns prefer using "kotimaista" (domestic) unless offered a big difference in prices. To Irish people Ryanair is domestic indeed. And being very well established in many other European countries RYR has just a figurative presence in Finland.
Having said this, maybe a base with the domestic staff would change it a little? On the other hand, also Brexit could force them to expand to other markets, so dear @Coochycool, let's just wait, interesting times ahead.