Despite a huge head start from Apple’s Siri, Alexa and the Google Assistant dominate the voice assistant field. Siri is extremely terrible.
Siri is frustrating. Ask her a question like "what causes brain freeze" and she'll return "I found this on the web". Ask her to "read page", or "read it to me", and Siri has no idea what you are asking, the context is lost.
Some critics think that Apple is too large, and thus is not able to innovate new products and services. The notoriously lagging performance of Siri is a perfect example of that. The 'AI' service misunderstand’s the user’s request, and often provides responses that are out of context. It can't read results to you and often falls back on "here's what I found on the web" which is not much assistance at all. Siri can hardly be called an Artificial Intelligence service.
Siri out of all the voice assistants, it’s the worst at answering simple queries and interacting with people and it does not stop there Siri’s limited ability to control devices is holding it back too.
Siri has been around for almost nine years, but it still kinda sucks. Google Assistant and Amazon's Alexa keep getting updated with cool new features, but Siri feels outdated and stuck in 2013.
The biggest problem with Siri today is that it doesn't integrate with third-party services very well. There are a few categories it does work with, like messaging or ride-hailing, but for the most part it's a closed-off ecosystem. This turns out to be Alexa's greatest strength. There are thousands of third-party skills and apps that work with Alexa, meaning it's a wide-open ecosystem where anything's possible.
Internally, Apple’s culture has extreme data and even physical barriers between teams. A person on the Watch team does not have authorization to enter into office space of the Siri team. As a result, Siri’s engineering teams are limited to work only within their team, and impact on the Siri product is extremely limited performance. Even simple tasks like integration with the Apple Maps team is cumbersome. This creates data and functionality isolation, and leaves gaps in ability to execute on new or cross-collaboration products. Without an ability to communicate with complementing product teams, Siri continues to exist on a non-functional island.
The final major problem with Siri is updates. While Google Assistant and Alexa constantly get better over time, Siri only gets significant updates once a year with new versions of iOS on the iPhone.
Siri sucks, and it will always suck, until Apple opens up its internal culture, and/or until their policy on storing customer data becomes a little more flexible.