There's no denying that Amazon's Alexa has a leg up on Google's Assistant, both because its smart speakers launched before Google and because Amazon has a huge footing in retail and the best marketing platform ever. Google can only dream of rivaling that. Plus, if you're a company making a smart home product, odds are you're already selling it through Amazon, and the jump from that to adding Alexa compatibility is just a formality at this point. The lead Amazon has taken over Google in the smart home is most apparent when you look at the number of supported devices, and now we have a more accurate picture.
Just yesterday Google was proud to announce that Assistant had support for 5000 smart home devices, up from 1500 in January. Not to let itself be outdone, Amazon has released its updated numbers: 12000 smart home devices support Alexa. The list is impressive and includes both certified "Works with Alexa" products and other compatible items. Overall, more than 2000 brands have added Alexa support to at least one product they make.
You can check the source below for the list, but it doesn't seem to include all brands and only one item per brand is linked, sadly. But at least, unlike Assistant's directory, you have a direct path to buying a product. Take note, Google.