(Though even if that is the case, I'd still think they could have at least agreed on open standards to use, to prevent anyone like Amazon from creating vendor lock-in.)
But Amazon had advantages from its size. In terms of economies of scale for device manufacturing, publishers could have somewhat caught up if they pooled money to invest in a co-owned company that made devices (though still wouldn't have had such an advantage as Amazon, who could share R&D and production costs with any overlaps to other devices such as smart home speakers, Android tablets, etc.) But Amazon was also able to take a bigger picture approach, using cheap Kindles/ebooks to attract people into their ecosystem and then converting a not-insignificant amount of them to buying other stuff on Amazon.