Because it's thought easier to replace what people might do with things we think might be people
It's not easier but it might make the punters and the employees more accepting. It's interesting to me that when this machine was "sacked" some of the employees were in tears (of sadness rather than laughter I presume) even though the end game must be to replace them with this machine's successors.
Personally,, I think the idea is ludicrous. If you want a system for directing people to where they need to go for certain goods, have a cheap tablet device that people attach to the trolley or, for people with smart phones, an app that does the same.