It solves the decentralized chicken-and-egg problem. You can't expect every appointment-place in the market to implement an appointment system that will work according to some common standard (which doesn't really exist yet), and the booking service isn't particularly useful until (and unless) a critical mass of service providers are compatible.
This approach, however, uses the "existing standard" (phone conversations in English or near-English) and can be eventually replaced by directly making an electronic booking for the places that will support it.
Offering a booking system to businesses is nowhere near sufficient, to offer this service to customers without being able to fall back to phone calls requires a near-universal adoption and that is an entirely different issue. This system can enable electronic booking even to places who don't offer electronic booking, won't offer electronic booking and don't want to do anything whatsoever to offer it, which in many domains means pretty much all places.
You can't force every service provider to use a web-based appointment system, but you can make such appointments without their explicit cooperation if they offer to do it over the phone.
Costwise it could be a simple matter of giving the software away and a cheap Chromebook. Creating the software is less complicated than what they are trying to do now and Google could easily justify the cost by the amount of data they could collect and getting a foothold in thousands of small businesses.
I feel like a large number of businesses already use software for scheduling but it’s a matter of having an API that can be exposed to customers that isn’t really supported. So it might be easier than you’re leading on.
A large number of medium to large businesses do. The overwhelming majority of small locally owned businesses don't. They still represent the overwhelming majority of sales.
Furthermore, big companies all implement their own software or purchase a variety of systems, some of which have API's, all have different API's and none have open API's.
A system that can speak, universally, to every Salon (or even say... 60%) is actually considerably less complex than the universal API you're calling "easier".
This will allow Google to confirm that their search rankings generate real revenue for businesses, so it makes things simpler for Google (and it is high-tech so that makes it cool! /s).
I swear every time this comes up it’s like people have never heard of open table or yelp, both of which handle online reservations for lots of businesses.
This approach, however, uses the "existing standard" (phone conversations in English or near-English) and can be eventually replaced by directly making an electronic booking for the places that will support it.