Nobody is suggesting that no one is in poverty and, yes, someone needing to use a food bank is in poverty.There are also many people in poverty who are not using food banks. All Mrs May was saying was overall there are fewer of them
Nor do people want to live on the streets, if fewer are living on the streets it does not mean that too many still are, and there will always be some, who are so alienated that they do prefer it.
We had one man locally, a friend did all she could to help him, but he did not want to be helped. Whatever had alienated him had done it so thoroughly that he absolutely refused to engage with those wanting to help him, presumably preferring life on the streets.
There will always be short term homeless; thrown out by family or partner, or temporarily out of funds who spend possibly a few weeks on the streets then get a roof over their heads again.