I really like the home app and homekit. But you have to use it for what it is, It shines at basic controls, and scene playback. Being able to control my house from anywhere by talking into my wrist is pretty cool. I mainly use this to start cooling the house down as I leave work (although not an issue these days)
the home app is also miles ahead as a dashboard.
Having a motion sensor being able to push a camera still as a notification to the lock screen your phone, even if they are from different manufacturers is nice.
And unlike in other areas, siri is pretty smart for homkit, She is able to exclude lights or rooms "Turn off all the lights except for the kitchen cabinets" and set relative levels, "dim the living room by 20%"
If you want to do any sort of involved automation or scripting though, homekit isn't the place for that. But Alexa and Google don't do well here either.
I use a home automation program called homeseer that has access to everything in my house. And then a program called Homebridge to get devices into homekit that don't support it natively.
Homebridge is a program that translates non-homekit devices into homekit. There are plugins for most smart devices, like TVs, cameras, smart vacs, thermostats.
My native homekit stuff like Hue is added to both homeseer and homekit independently.
my non-native things like Z-wave wall switches are added to homeseer, and then I use homebridge to get them into homekit.
Since everything is in homeseer, I can script things that need it there
I have a virtual thermostat for my bedroom ceiling fan, it uses a temp sensor, and will adjust the fan as the room warms or cools, That all happens in homeseer, but I can use Siri to control it, I can either set the fan speed directly, or set a target temp.
An option to homeseer is home assistant, which is another home automation software, but it basically has homebridge built in, so you can add devices to homekit directly from that software
Homekit not being included in devices, is squarely on the various manufacturers. The protocol is open to all, although my guess is the licensing fee per device is probably higher for homekit than it is for Alexa. Which is why you don't see homekit in lower cost products.
It's not that Apple hasn't put homekit in X device, it's that the people who make X device decided not to put homekit into it.