The company did study the Echo closely when it showed up in 2014, but dismissed its lackluster audio quality and set to working on something that sounded better. Beamforming (which directs sound based on the shape of the environment) was key to that strategy, but the exact shape and components didn't coalesce for a long time.
Then there's the question of priority. Apple appears to have always treated the HomePod as an accessory, rather than a platform like Amazon's Echo line. For Amazon, the Echo was its primary way of getting Alexa (the real star of the show) into your home; for Apple, Siri on the HomePod was just one of the selling points. While it seems like Apple treated Amazon as competition, it just wasn't in a rush to create a living room AI companion.
Whether or not that's a problem isn't clear. Even with the HomePod's delay to 2018 and $349 price, Apple is reportedly expecting to sell 4 million units in the next year. However, the Bloomberg piece suggests that Apple's relative lack of commitment to smart spakers not only kept it from launching the HomePod in a timely fashion, but may have given Amazon (and Google, for that matter) a long-term advantage in AI. If voice assistance becomes a household must-have instead of a luxury, Apple may have to scramble to keep pace.