Churches (specifically Christian churches) can be dead center in the culture. Or they can be solidly Christian, and still be countercultural. They might say things like:

You're looking for social unity? Politics isn't going to create that, no matter which side wins. We can show you a real social unity.

You're looking for security? The government's Covid response isn't going to give you that, even if they do it perfectly. We can tell you where you can find real security.

You're looking for happiness (or, more deeply, for joy)? You're not going to find it on Facebook, or at Walmart. We know where you can find it.

Now, you may think that Christianity can't actually supply any of that. But it claims that it can. And the point is, that claim is very countercultural.

Some things that count as churches may have sprung up to make such offers, but I am assuming most churches have been standing since before Covid, before Facebook, before Trump and Obama and Bush.

If say 40% of people are attending these gatherings, it's a tough sell that they are so far from mainstream as to be countercultural.

People have been visiting churches in search of unity, security, and joy for thousands of years.

And for thousands of years the churches have been saying, "The culture isn't going to give you that."

I don't understand why churches would say that, when they were the cornerstone of culture until a few tens of years ago.

Traditionally, they say that because even when their outward trappings are all over popular culture, they know that their core message is difficult to live out in practice, and most of the people who show up aren't doing it.

I think AnimalMuppet is talking about more evangelical churches, whereas you are talking more about what used to be called "mainline" churches.

I think that's right.

Before about 300 AD, they weren't the cornerstone of culture. In much of the world, they never were.