I'd like to add that I use tools from fivefilters.org daily. (Mostly Push to Kindle) If the authors are on this thread, thank you so much for making these tools free to use and for such consistent uptime.
It's possible service development is happening very often, just not in the dev circles I spend time in. (web based startups)
Regarding writing interfaces for the service, that's fine too. It's just an easier way to integrate with a service. But there's a big difference between writing a service interface and a library that implements the service's functionality.
We do have plenty of open source services (e.g: Zookeeper, Redis, Kubernetes), but few product level like Stripe/Auth0. Yet there's a lot of duplicated effort in things like writing ecommerce/forum/blog/geolocation/social software. I wonder why we don't have more of these.