The number of posts usually reflects how long it has been going for. So for pet threads, they will just rumble on over the days/ months/ years, whereas a post for a very specific person or situation will usually have less responses because it is active for less time.
And of course as people get to know each other it is natural they stick together and celebrate each other. All of them were new members once and chose to stick around! Of course not everyone does and that’s fine too. We all have our own needs and will find them met in different ways.
When I joined I spent my first month or two reading around and getting a feel for the place. It made it easier to join in. Not that there is anything wrong with being active right away! But there is so much helpful info and I would highly recommend soaking up as much of it as possible!
For you or anyone else new to the forum, this is a good place to start 