

It’s a good tactic because whatever lies the Whitehouse comes up with to defend against the first few leaked things might be countered by the next few leaked things. They have no idea what is available to be leaked next so have to be careful what they say.
If it all came out at once they would know exactly what they have to work with when crafting their story.
As well, coming out a little bit at a time means people can focus and pay attention to the details, discuss it.
If 20,000 emails were all of a sudden leaked hardly anyone would care because no one would be talking about the same things at the same time and the details get lost


And more
They also shouldn’t be allowed to do anything political on their personal accounts, such as trying to get contributions or clarify political stances, etc. if they have any potential constituents banned or blocked