We were told by the boat guide, that these homes were ones which had a government caveat on upgrading. I think the idea given was that the people weren't really poor, but the government refused to let them sell or upgrade on pain of acquisition. It sounds a bit unlikely to me, since the government elsewhere has no compunction at repossessing properties they deem necessary. Sooo, I suspect the story is given out, to assuage tourists' horror at the squalor they are seeing.