I did not want to, either. 
However after spending like a year investigating commercially available Zigbee mmWave sensors and still not really finding any that met my needs, I am seriously reconsidering this stance (as in total, DIY may have actually taken less time(!)).
Also your particular combination of wants is (at least to me) pointing in the direction of DIY. Maybe not what you wanted to hear. But hear me out…
mmWave needs to be powered all the time, so PoE would be nice for that. But the next level in Occupancy detection (after mmWave) is to start asking “who?” is in a given room. And then you are looking into something like Bermuda (or similar BLE trilateration). Combining the two, I think, might be the Holy Grail of Occupancy detection.[0] And good Occupancy detection is the cornerstone of many (almost all?) Automations.
Something else related is light level detection. Which many Zigbee (PIR) sensors only send when Motion is detected (and some mmWave, like FP1E, do not send at all!).[1] Another reason to have an “always on” sensor. So if it is overcast, the lights can come on, even though it is the middle of the day.
You probably might not realize all of this until you get a year or two into your home automation journey. And by then you will have spent a lot of money and time buying many different devices. This is where I am at now. And I have been a strong proponent of Zigbee (70+ devices now).
However slowly I am realizing that ESPHome seems to provide everything I am looking for. I want an all-in-one sensor providing mmWave, light (lux), and a BLE beacon (for Bermuda). And the only way to realize that is with ESPHome.
Now, there are a number of commercially available multi-sensors based on ESPHome. Maybe you want to go that way. However, personally, I find almost all of those to be ridiculously over-priced for what they are (as ESP32 and these sensors are only few bucks each). And none of those (to my knowledge) are PoE.
Which brings me to your main requirement, PoE. Which I think is actually a pretty great idea! [2] However there is very little COTS[3] PoE IoT[4] products available, at least that I am aware of. So now we are back to rolling our own. As there are PoE ESP32 modules available, and then you can do whatever you want (and also, modify in future, as needs inevitably change).
ESPHome makes things pretty easy, actually. It’s a very nice project and was a great idea. This is “low code” and just following some simple step-by-step instructions. Not like programming Arduino from scratch in C.
I think you should do yourself a favor and at least take a look at the project.
[0] Although I have yet to achieve this. I will let you know when I get there.
[1] Which is really a shame, as otherwise this was the best mmWave Zigbee sensor I found so far which meet my requirements.
[2] Due to all reasons mentioned above with always on sensors. But also BLE beacon monitoring can take up a lot of bandwidth, which therefore might be better to do over Ethernet than Wi-Fi.
[3] Consumer Off The Shelf
[4] Apologies for that acronym salad. 