Jeremy Corbyn is popular in the Labour Party because of his position on the political spectrum. For example, he is not likely to invade Iraq or Libya or anything like that and he is in favour of nice things and so on.
However, he is reading from a script and one that was written decades ago. He doesn't want to talk about Brexit because there was a time when the Labour Party was against Europe, he was part of that and he does not want to be described as a turncoat.
We are talking about a part of the politic spectrum where suspicion, paranoia and accusations of betrayal are rife.
While I might agree with him on a lot of things, he is just an incredibly weak leader.