While yeah, these old robots could in theory do more than an echo watch some of the videos of them in operation (eg: https://youtu.be/oibgyqdXfJM).
Just take the voice on that youtube video, while impressive for the 80's is no comparison to Alexa's voice. It is very slow and has a thick robot accent. Alexa has a much more dynamic, fluid voice that is much easier to understand.
And yeah, I'm sure some of these things could be commanded by voice, I imagine that you have to be extremely precise with what you say and how you say it. I imagine the error rate is way higher than Alexa (which in my experience is pretty high itself).
I dunno where I'm going with this comment, but the interface matters. It's easy to claim "they were doing all this shit back in the 80's" and it might be technically true, but how they were doing it didn't have nearly as much polish as modern stuff. When you have a 4mhz processor and 64k of ram, there is only so much polish you can add to an 80's robot. The echo dot has a quad core processor and 4gb of ram -- not to mention wifi, bluetooth and gps (https://www.digikey.com/en/maker/blogs/2017/amazon-echo-dot-...). You can add a lot of polish to a hardware stack like that.
Of course, even with all that processing power, I'm still only about 50% successful turning the lights on at home. We still have a long ways to go....