Home Assistant is product agnostic. It interacts with 1800 different devices and services and all integrations have access to the same Home Assistant API. There is no preferential treatment.
To get these devices and services integrated we rely on APIs to interact. These APIs are provided by companies. In the case of Tuya, they once had made an undocumented API and contributed this to Home Assistant. The person responsible for this unofficial API left Tuya and the integration maintenance has been taken over by a Home Assistant community member. However the API starts being less and less reliable (throttling when called too often).
In the meanwhile Tuya has created a new documented official API (they call it Open IoT platform). It integrates more devices than the old API and it is push based, meaning updates are near instant.
They want Home Assistant to migrate to this new API and shut down the old API so they create a new integration for this. The old API is going to be shut down, the new one is the future, so we obviously want this in Home Assistant.
Our collaboration with Tuya extends to the fact that we gave pointers on how to structure their integration, reviewed their PRs and helped make sure the documentation is great. We do this with every contributed integration. We also invited them to the release party because this is the first time that a company of their scale invested engineering resources to create a Home Assistant integration. We have invited other contributors in the past too. There is no contract with Tuya.
If certain devices are not supported or don’t work as expected, that’s a bug introduced by Tuya and as always, we’ll work with the code owner and the community on addressing those.
People saying that us working with companies on integrating their products is a bad thing do not understand the very nature of what we try to achieve with Home Assistant. Home Assistant’s goal is to be the platform for your home that can include all devices and services. Your Home Assistant installation fetches your data from cloud platforms and local devices. It gets it all locally and goes from there to offer dashboards, automations etc.