Different people at different stages in life seek very different things in their (poly)amorous relationships.
Say, you are in your mid-20's. Say, you live in a metro area. You are a reasonable dude, and want to enjoy your life, build up your career, buy a first home, etc. You are really not expecting that your LTR will last for the next 30 years. It may, but the chances are that it won't.
You are focusing on the fun part. Reliability is fine but this is really not your main concern. You, and your partner(s) know that you are going through a transient phase in life. So, being polyamorous addresses your need to date, romance and yeah, have sex with a group of 2-3 other people whom you are emotionally attached to in this stage of your life. You are not into the ball-and-chain relationship kind. And you also do not feel like cruising every night to meet yet another, probably unknown dude with whom you may not have any emotional link whatsoever.
You want to do things, go places. You have your plans. One of your partners shares some of your interests, but not the others. Why force people into watching football games if they are really into classical music?
So, a complex relationship pattern develops.
I used to date a dude I was going to college with. He was fun to be with, and we spent hours working on our school projects, making sure that we pass our exams, make it to dean's list, etc. Both of us liked two other guys both of whom were in the deep closet. Their time with us was pretty limited. One of them was happy to connect once or twice a week for a hot sex session. The other one was a free dude who chose to stay in closet, but was happy to hang out together with anyone of us, make short trips, and enjoy the company, dinners, concerts, whatever and whenever he felt like it.
There was still a huge amount of giving and taking involved. But it worked pretty well for all of us for a couple of years. Which is a long time in a life of a postgrad student
. Then the life interfered as it usually does. One guy got married, and moved on. One dude got a job in a different town. I moved on to live and work abroad.
Parting with the guys was not easy. But we all saw this coming. Everyone agreed though that we had had some great time together. There were stories to be told, and some awesome sex to be remembered.
Would I do it again, under the same circumstances? Yup, at a drop of a hat.