Interesting. Is this a debating tactic?In a two party system, one party moving to an extreme doesn't compel the other to move to the opposite extreme if there's a genuine appetite for the centre ground. It's just not logical.
When the labour party moved to the extreme the conservatives had the option to remain moderate or move to the extreme. If labour had remained moderate moving to the extreme wouldn't have been viable because labour would have picked up almost all the centre votes. By moving to the extreme labour and the conservatives made pretty much the whole of the centre swing votes. The conservatives proved effective at using a disaster they created (brexit) to shift swing votes in their favour which was remarkable given their social and economic record while in power. It is hard to overstate the ineptness of the hard left controlled labour party.