What are the benefits of organizing a conference? Organizing a conference is very difficult for a scientist, you have to have the right collaborators, to find the right venue, to spread the word, to advertise it, to send the call for papers, to receive the papers, to check them, to organize the lunchs and dinners, etc etc.

All these tasks are very time-consuming, and stressful, and they will steal precious time to your scientific research activity, and also to your family/friends time.

So, why do people decide to organize conferences?

What are the main benefits and advantages of running this complex and time-consuming activity?
If everyone refused to organize conferences, we would have no conferences.

Yes, it's that obvious.  The same goes for editing journals, refereeing papers, and most other service activities.

The main result of a research conference is that it helps attendees do better research, to find and understand new ideas, and to disseminate their own research, etc.  By organizing the conference, you are the facilitator of all that.  Furthermore, you get to influence the direction of the conference -- what it will focus on, who the invited speakers will be, how it will be run, and so forth.

Additionally, I would argue that academics are paid to organize conferences in the same way that we are paid to referee papers.

Finally, there are fringe benefits to you personally, including the prestige mentioned by @user3209815 -- you can list it on your CV under service activities.  Frankly, this is not going to make or break your career, and you probably shouldn't be doing it early in your career, since (as you point out) it takes time away from things that may be more essential.