One theory could be that unlike Apple, the Android market is fragmented and unless you're the (relative) minority with Pixel devices bought directly from Google

One theory could be that unlike Apple, the Android market is fragmented and unless you're the (relative) minority with Pixel devices bought directly from Google, you depend on your device manufacturer and/or the carrier to include any announced features. If you see something at an Apple keynote you know exactly when that's landing. If you see something at a Google conference, it's much less clear when you can take advantage of it, if at all.