If I have my bathroom door closed, Echo can't hear me from the living room unless I yell whereas my iPhone is usually with me. Also, I can practically whisper when my iPhone 6S is next to me to turn off the lights so as not to bother anyone. You can't do that with an Echo in another room. There's a reason why Amazon released a smaller, cheaper version.
And that's my point. With all these personal devices which are usually close by or worn in the case of Apple Watch, I don't think an Echo clone makes sense for Apple. It makes sense for Amazon because they don't sell a lot of mobile products.
Also, Echo's speakers are crap compared to good AirPlay speakers so I'd rather Apple expand Siri and HomeKit so I can tell any Apple device to play whatever song/artist/album on any Airplay speaker I have in the house which would be a far more powerful solution than another Echo clone.
You can - actually. With Echo's remote and their app.
We differ in opinion. While you may not find it of use - it makes sense for Apple to have a device in this space. Especially for combining homekit and a smart music player. And one thing Apple could do is make it so when you play music - you can do so via airplay speakers instead of its built in.