Well, WRC2 has professional-level competition and the rallies are long and expensive. I heard in the Absolute Rally podcast that a WRC2 rally costs roughly double the amount of an ERC rally. And doing national rallies in some country (Italy, Finland) would probably be even cheaper. And competition-wise, it's good to learn to win, to build mental strength on keeping a lead and finishing a rally under pressure. It's easier to win a national rally or an ERC round than in WRC2.
Of course, you have to go to WRC2 at some point if you want to be a professional, but if your career is at the point where you want to learn different types of roads outside your country, it just doesn't feel like a cost-effective idea. If you have the budget/backing and modest results won't take that backing away, then no problem.