Can they? Are there many rooms going for > €1000 a month. The going rate where I am, in Dublin, is about €600pm.
Plus you're not just renting the room. You're sharing the house. There is some inconvenience in that.
I'd argue it from the point that a landlord has much less rights than somebody renting to a lodger. I looked into renting a house out a few years ago. The risk to me wasn't worth the reward so I didn't bother.
For renting a room, we didn't want to do it at the time but after doing it for a few years now, we're happy to do it forever.