(1) because she publicly represents their “leftist” “be kind” worldview, so their own worldview feels under attack if she is criticised
(2) because she presents herself as fragile and marginalised and in need of protection. The squigs of (1) see her as the type of multi-marginalised individual they should be “uplifting” and righteously defending
(3) because they’re middle class and they don’t have a clue what working class people look like. Also, they’re all supporting each other’s working class identity delusions
(4) because middle class leftists are often ignorant of the fact that their worldview is uncommon among actual working class people. Because middle class leftists hate people who don’t think exactly like themselves, this makes them subconsciously hate working class people. They are relived to find in Jack a “working class” person who is just like them, which relieves them of the cognitive dissonance of finding that they always hate working class people, while identifying as somebody who supports the marginalised.
(5) People on Twitter think that Tweeting is activism. So by defending Jack, they are being an activist and protecting the marginalised and making the world a better place.
(6) I think some are simps who fancy her.
Oh my this is all so true. Especially point 4. In my experience (and I appreciate this is not representative) as a WC girl who started properly encountering the MC and UMC at uni, first in my fam to go, I found that MC people have a very weird idealised idea of what WC people are like. It's a fictional ideal basically created by Ken Loach. The ideal WC is a nurse, international socialist, goes on Pride and anti-racism marches, swears and drinks a little bit but basically is very well-behaved, respectable, community minded, and above all ever so grateful to their bien pensant MC overlords.
None of the actual working class people I grew up with are much like this. They appreciate family, location, community, financial success, the acquisition of material goods and awesome travel experiences, sharp (and often uncomfortably personal) humour, good banter, good music and sport. Showing the proper amount of mutual respect is very important, as is straight talking. If you default on either of these things, they will not easily forgive you. They're a good bit less racist or sexist than MC people I've met, although they might side-eye you and demand to know exactly what you mean if you tell them your pronouns are xe / xir. They might've voted Brexit, they might've thought Corbyn was a bit of a woolly wally. Or maybe they didn't. You know? What they're not anything like is the cringe-worthy portrayal of the 'honest respectable working class' in terribly worthy BBC dramas. And that's fine. There isn't just one, approved way of being in the world.
MC Guardian types, the Nigellas and George Monbiot and Zoe Williamses of this world, don't understand any of this and it scares them. But with Jack they have a nice, colonised, 'safe' 'WC' person, so they can virtue signal by showing her love on Twitter without having to take the risk of engaging with a real WC person who might start asking them difficult questions (anyway it's OK; there aren't many WC blue tickers on twitter, or in media these days full stop).
It's disgusting really - no one these days would get away with idealising and misrepresenting POC this way, and rightly so. But it's OK when it comes to class.