But first of all, I think it does a general disservice to classify people as falling into only one of two limited categories, "conspiracy theorists" or not. That approach is itself unscientific. (But psychology is half silly science, in my skeptical view! And now I'll try my shaky hand at it....)
I think things occur far less by accident than one may believe. This is based upon observing patterns in history, wherein events transpire seemingly for defined and / or advertised purposes, but admissions occur later as to the true motivations, actions, techniques, participants, etc.--and even the results--involved. These admissions often reveal significant departures from the "stories" of the day. History is always a retelling colored by the teller! (And motives exist more often than not. This you know.)
Even a rather unsophisticated awareness of this "dynamic" in human society / history causes me to be skeptical of "official" stories, at first at least. I mean, look at the degree to which we are advertised in our society. It is staggering. It is all product placement, etc. This is intentional manipulation. The same techniques are applied to cement other concepts in society. This is all well-known. Propaganda is real and we know it played a part in motivating people to make sacrifices for things like wars, etc. in our past. Propaganda is intentional manipulation. We know that truths (ie: casualty figures from battles in WWII) were / have been kept from the public deliberately. For our own good? Perhaps. For morale (a shared mental-emotional state that propels us to "stay the course")? Yes. This is not difficult to distill. Government has engaged in this. We all know there have been cover-ups of politicians' bad behaviors / illegal actions before, too.
So, if governments have been proven to hide things / act in secrecy from the citizens they are supposed to serve / represent, well _____ . You know what the possibilities may be.
You have to consider information: what we get from whom and where it comes from. Its delivery is not at its best when literally a handful of organizations own all news outlets, etc. (Look it up.) It is a severe handicap with which we must all deal.
Your comment on a lack of empirical evidence merely shows you need to learn more about that which you attempt to criticize. Come back when you've done your homework. [Are you in your 20s?] Yes, there is much speculation rampant, but there is a lot of empirical evidence thrown about, too. (More of the latter when it really counts, I should think.)
Motives exist in connections between organizations, people, etc.. So, too, to be fair, are pure coincidences. Perhaps there is a way to quantify the proportion of connections which have indisputably resulted in conspiratorial actions / policies / results versus those connections which are clearly harmless and / or have not resulted so? [Hmmmm..... Worth some thought.]
Your question about why people do little to nothing is the best point you make. There are many people trying to take action. Problem is, those people must observe and act within the confines of law, while conspirators, by the nature of their activities, break the law / operate outside of it. (Capone was a conspirator in many ways, mind.) But beyond that? Fear? A feeling of helplessness? Dunno. Again, fair question. What can they do when society has been trained at large to shun the skepticism of a minority group?
One of my degrees is in an empirical science. I think scientists are occasionally some of the stupidest, thick-headed people I know! Arrogant, certainly. Even self-deluding at times. Ironically, science can become a crutch for intellectual laziness. (I include myself here!) Don't pat yourself too chumily on the back over your status. Many real things are as yet unexplained by science. It doesn't mean they are not real... just because we scientists are too ignorant / without the appropriate technology / metrics to measure and vernacular to explain them!
It is true that some folks become addicted to the study of conspiracies / far-fetched theories / forbidden knowledge or the quest for it / etc. Fear is itself addictive sometimes.
Make sure you know clearly what a conspiracy is. Then learn what a conspiracy theory is. Then learn what a conspiracy theorist is. If you are going to smush it all together, well, you'll be quite off track, to say the least.
Any good stuff here? I hope I've helped. If not, no biggie. I like to hear myself "talk" just as much as the next guy...
And welcome, if you are sincere. If not, prepare to metaphorically get your ass kicked here.
What would the Founders do?