They created it after seeing how effective the intercoolerjs/htmx approach was for their web application.
Hypermedia is a neat approach to building applications. We should look into it more.
One big difference: instead of JSON, we use XML to represent the UI. XML is a hypermedia format with built-in extensibility, which makes it a good fit for server-driven UIs. We wrote about this decision here: https://engineering.instawork.com/when-xml-beats-json-ui-lay...
JSON has a data model based on the lowest-common-denominator data structures available in programming languages, i.e. lists and dictionaries.
HTML/XML has a radically different data model that's based on documents that are filled with content with intermixed markup/metadata.
As a result, representing pure data is awkward in XML but straightforward in JSON, and likewise representing a document of mixed content is very very awkward in JSON but quite straightforward (and easily extensible) when represented as XML.
It's one of those "use the right tool for the job at hand" kind of things.