I failed with two facebook groups. How do you create an engaging fb group?

I made an fb group to discuss about gadgets. We gained 20k members in 6 months and initially the discussion was good, around gadgets and everything niche but then people got bored and they started discussing random things, putting random things (cat videos etc). We moderated the group but no one seemed much interested about gadgets anymore and we had to close the group after 1.5 years.

I made another group about digital marketing and it has 100 members. We are consistently seeding posts and we are seeding comments too but none of the members are participating as there are hundereds of other groups for it.

I am not sure how people make a success facebook group. Can anyone guide me here?

Im not extremely experienced with Facebook Groups, but would it have been a possibility to just change the name and theme of the group to match what your members were posting rather than closing it?

In the Facebook groups I'm in that are very engaged, there's a clear leader in the group who frequently does lives and offers a lot of value. I don't think it's enough to just post a half-hearted piece of information or a link to a gadget - I think you really need to put yourself out there.

I'm in lots of Facebook marketing groups and most of them are very inactive. The ones that are very active are typically centered around a specific product or industry. And the head of that group frequently shares insightful information about the main topic of the group. The groups I'm in where no one participates are things like digital marketing for XYZ industry. Because there's not a focused discussion or program, people just drift away and it ends up being random people posting random links to buy discount Ray-Bans.

I'm wanting to get into group management and marketing myself and I am certainly not an expert but coming from the perspective of an active member of many groups, those are the things I see with the groups I'm in.