I mean you're right, but also Google had one of the legitimately best options at the time and massive visibility and seemingly credible institutional commitment. And it was early to a scene of web based always online RSS readers when before that they were typically desktop-based. And on desktop portability was achievable but not as convenient. With reader it was nearly effortless.
While it was definitely possible to use alternatives, it effectively became king of the mountain which gave it the power to deal a punishing blow to RSS once they pulled the plug.
I will just say it was a very different time and at the time I didn't regard Google as a place that didn't make credible commitments to new products. But big picture I think you're right.