So, non-sequitur thought. Why are centre-left members considered Tory-lite, rather than centre-right members being considered Labour-lite?
The US has purity tests in play on both sides with the RINO's and closet Republican neoliberal oligarch Butcher of Benghazi.
The Tory-lite or [insert main conservative party]-lite rhetoric is widespread all over Europe within the left wing political circles partly because of history. When we track back to the origins of labour movement the struggle was much more ideological, it was there to change the establishment of capitalist state and to liberate the workers by forming new form of governance. Even up until 70's and early 80's it was still common to hear left-wing politicians and parties state that the ultimate goal is in fact building the socialist state.
This has changed of course, partly because of increasing wealth, globalization and the end of cold war but also partly because of the success of the welfare state. Center-left parties have adopted a different approach over time: because capitalism didn't fall and could not be toppled, the aim is to accept and reform it to be more socially just. Now, this is not a new development as it basically started in late 1800's with
Eduard Bernstein being one of the pivotal revisionist theorists within the movement, during most of the 20th century there was a huge debate over what is the correct path forward. It was only in the last decades when the concessionist view really took over.
Tory-lite is basically a slur used against people who have adopted these views. They're in cahoots with the establishment that they should be fighting against so to speak.
Why isn't it the other way around? Well, to put it simply they have the advantage of being viewed as the aforementioned establishment.