Conservatives upset?

I'm reading "White House roasted for saying Biden will give a ‘big boy press conference’: ‘Potty training next?’/Conservatives upset by ‘unbecoming’ joke in Monday’s White House briefing" (Independent).

Today's the big press conference that the White House referred to as “big boy press conference.” I would think that joke would upset Biden supporters. The idea of the press conference is, ostensibly, to give Biden another chance to prove he has the ability to serve as President. To tack a silly name onto the event is to undercut his effort. People can't stop saying "big boy press conference." Aren't conservatives just laughing?

In Monday’s White House press briefing, John Kirby, the White House’s national security communications adviser, raised eyebrows with his choice of phrase....  “The president will hold a press conference… a big boy press conference we’re calling it,” he said....

It's as if they've internalized Trump and are using his style of trash talk... against themselves. 

Kirby’s tongue-in-cheek reference was actually a callback to an exchange last week between [Karine] Jean-Pierre and Bloomberg journalist Justin Sink, who had asked her about the White House’s alleged strategy of shielding the president from “impromptu” settings in light of his disastrous presidential debate performance. 

The press secretary had denied that Biden had anything to hide regarding his competence for office and duly promised a “solo” press conference from the president, which prompted Sink to ask for more specifics: “Is that gonna be kind of the real, big boy press conference that we’re used to or…” 

“Did you just say ‘big boy press conference’?” she responded, as fellow members of the press corps broke up laughing. “Big Boy Justin over there… was asking some big boy questions,” Jean-Pierre joked.

Oh, Jean-Pierre must have thought she got the better of the exchange. She made a riposte. And then Kirby thought he could be funny — in an inside joke kind of way — by making a "callback," which maybe seems like a cool comedy move. Wikipedia:

In comedy, a callback is a joke that refers to one previously told in the set. It is also known as an internal allusion, a literary device that helps give structure to the piece of writing. Callbacks are a subset of inside jokes....

Meanwhile, the whole world is listening, and we didn't notice the comic resonance with what Justin Sink and Karine Jean-Pierre said back and forth to each other a week ago.

The Independent article continues:

A viral clip of Kirby using the phrase on Monday nevertheless prompted plenty of context-free ridicule.... 

Oh! You want to ding the ridiculers for omitting the context? But Kirby omitted the context, when he deployed "big boy press conference" as an inside joke.

Inept. I get the joke. The country is, apparently, led by a man of limited mental competence, but we're supposed to be amused by an inside joke that perpetuates the idea of him as a child. He's a child but not a baby, so that's funny... because it was funny a week earlier. Which you ought to explain every time you repeat it, otherwise you are indulging in "context-free ridicule."

And I still don't know why conservatives are the ones who are supposed to be upset here.