Perhaps eventually, they’ll need to once the network effect takes hold.
But I asked myself the same question. I think vendors could distinguish themselves by offering special deals to people who specifically sign up for their instance, a tiered membership plan, payed memberships, etc. Maybe exclusive items for members only.
I’d be interested to hear more ideas but right now, that’s the gist of the benefits I can see. The other obvious benefit I can think of is the inclusivity of it all. If this idea took hold, it eventually wouldn’t be wise for vendors to abstain from using this service once customers are using it to find places to shop….and since it’s free, it isn’t something that businesses have to worry about like they do with other services like this that charge those businesses in order to list them.