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.