How can I better build up my Facebook group?

Hello everybody,

I am co-owner of a Facebook group which was created in October 2018.
This group has no specific topic, it's a group to meet new people and make friendship with them.
It has now round about 2,800 members.
This is okay, however, I would like to grow the group even bigger.

So there is something I don't understand:
In the period between October 2020 and April 2021, we had a lot of Facebook users coming to our group. Some days, we had up to 20 membership requests from people...

How can I better build up my Facebook group? WordPress ...