I like the saying, Polyamorous relationships are just like Monogamous relationships, only there are more people.
In polyamory, you can definitely have everything you would "expect" to have from monogamy, and often so much more.
For example, suppose you have two serious boyfriends, and suppose one day you learn some bad news that puts you in a personal crisis. You will then have not one, but two boyfriends who love you and be willing to drop everything to come support you. Or if one of them happens to be away on business, the other one will still be there for you.
This is just an example and is by no means "the reason" to "become" polyamorous, but it is definitely an advantage over a monogamous lifestyle.
“As I am sure any cat owner will be able to tell you,
someone else putting you in a box is entirely different
from getting into a box yourself.” —bisexualbaker