Thanks hoser, this is the perfect conversation to illustrate my point. That you have decided not to take part in Facebook is actually a great help in this regard:
I believe you carry (an understandable) assumption that is essentially, 'Well, Facebook is the preeminent site everyone has gone to, they left places like this so therefore it must have some things going for it, and certainly something like being able to search the content would be an afterthought.'
Unfortunately, this IS COMPLETELY WRONG.
Just look at the results from the link you gave. All of the results are either "Group" homepages, profile pages of companies, or "Marketplace" ads. None of the search results from this link include any of the actual content from the groups themselves (e.g., individual posts).
"Well, this must be because the search for "FL400" is such a general search that, of course, nothing but very general results will be listed"
So, what happens if we make the search more specific: "fl400 drill piston" -
https://duckduckgo.com/?q=site%3Afacebo ... fab&ia=web - what results come back for that? Absolute *shit, with nothing relevant to the subject at all, and more specifically NO GROUP POSTS (again the individual content people are posting).
You're not missing anything, there is nothing that anyone is "missing". Facebook does not allow indexing of individual content (by using robot.txt files and other means) and does not not even provide a remotely useful search function of its own content. As I keep saying, after a post goes off the front page of a group it is all but disappeared for future use/discovery.
Why is this happening? Because Facebook has somehow calculated that it is in their interest to direct attention/eyeballs/clicks in other ways. imho, the bigger question is why have so many motorsports enthusiasts mindlessly gone along with this and not realized at some point that their content is being flushed down the toilet along with it's/their chances of being 'found'.