How do these accounts grow so large while being private

I've noticed lately there's large meme and fan accounts that are private. How are they able to get a large following while being private? And is there any benefit to going that route?

Viral content.
They simply focus on the content so people start sharing them and new users will have to follow to see the content.
Also , you need to focus on your bio and profile pic

They grow with shout-outs for shout-outs which works wonders if your account is private.

People are more likely to follow when it's private. The sense of secrecy creates an urge in people.

I have few friends in meme niche, they are doing great gains with bait shoutouts and shoutouts for shoutouts.

I am on Instagram for years, lately I've decided to turn two of my big accounts private due to the new policies and my followers decreasing. Guess what happened?

1st account is having 300follow a day and I went from 301k to 305k in 3weeks
2nd account I checked yesterday with 800follow requests in less than 20h, went from 290k to 311k.

Here is why: when you open your account to the public you might get targeted or reported.

Regards