Apple has never been the "de facto standard" for any of its products, nor does it want to be. There are over 1.5 billion Apple devices in use worldwide, and those users are more likely to use Siri and HomeKit than the alternatives.
You make a valid point. It just would make so much sense if they introduced HomeKit in such a way that third parties would have more easily supported it. And made it more robust and reliable. That would have strengthened the position of their iOS devices. Instead, they let Amazon and Google introduce cheaper devices that are more easily supported by third parties. I would assume Apple is scared of that. After all, there missing out on a USP for their devices, and letting the smart home market slide. But what do I know, they’re the biggest tech company in the world. Meanwhile, I have 7 apps for smart devices not working together.