IoT products exist to connect with products from other manufacturers. To interoperate, those products have to agree on how they communicate. Today this almost always done using open standards like MQTT, BLE, HTTP, TLS, etc. They need to share data in common formats, like JSON.
IoT software is usually locked to one manufacturer's silicon because all the APIs are provided by the manufacturer. That means switching to another microcontroller can mean a near total software re-write. Over time, this prevents companies from adopting the best silicon available for their products - resulting in higher costs, lower performance and a competitive disadvantage.