Yes - the lack of G+ API was a big mistake not just for consumption but also for publication.
However, both Twitter and FB had lists long before G+ was even a thing. Twitter has done little/nothing to promote the list functionality other than to increase the 500 member limit on lists. FB went head to head with G+ Circles by enhancing the FB list functionality to include standard lists and school/workplace lists.
I wasn't going to stop posting on FB, and I wasn't going to write everything multiple times.
Being able to feed from FB to G+ would have at least meant I could be active on both sites. As it was I had to pick one, and FB had a lot more of my friends on it.
However, both Twitter and FB had lists long before G+ was even a thing. Twitter has done little/nothing to promote the list functionality other than to increase the 500 member limit on lists. FB went head to head with G+ Circles by enhancing the FB list functionality to include standard lists and school/workplace lists.