If you get the right collaboration partner it's a "the whole is greater than the sum of it's parts" thing.

I've been working with a songwriting partner for more than a year now, 14 songs together so far. We both bring a skill set to the table that the other doesn't have, or is weak in.

Plus, as rharv said, it's fun! We have a blast working on the songs together, there is a lot of back and forth banter as we develop each song. She is in Germany, I am in Canada, so this is all done by email.

Music needs to be fun (for me) or there is no point whatsoever to do it, there certainly isn't any money to be made.