Here's an option I used in mine. 3.3V fixed regulator and they are small enough to fit inside of a 3d printed CR2 "battery" I paired these with a micro usb socket. I can use any microusb cable and phone charger.
https://www.amazon.com/Partstower-Step-Down-Supply-Module-AMS1117/dp/B01FWFSTBY/
https://www.amazon.com/ZXUEZHENG-Pinboard-Interface-Adapter-Breakout/dp/B07KS1RPMP/
Here is my version of hardwiring them. Since many of mine are plugged into outlets in the attic being able to remove the “battery” to reset it was useful to me.
The USB hacks that these guys have reminded me are possible were less interesting over a year ago....as the device count increases I'm interested 
Although...if everything reliably sipped juice like the Iris Motion that would be nice. As has been said by the OP and you, the Iris battery sipping design is more valuable than their price tag!
I have some older Visonic security system motions which use the same battery and are also sippers ....but I expected years out of those because Visonic spent years refining those sensors and they weren't cheap. (That system tells you when a device has poor signal or hasn't been heard from, but I have one sensor in an infrequently trafficed area that must be on 4+ years and I find myself leaving the system armed just to trigger that one occasionally because I can't believe it's still going! Yeah there IS a sensor health check that I could run to check them all but it's easier to just trigger it.) 
It is interesting how the Iris designers (and a few others) realized how much of a hassle a full topology of battery driven HA devices would be if the battery wasn't long lived... while other shops didn't give this the attention it deserved and were more about making some small cool Swiss Army knife device that runs (out) on a coin battery. As if 10+ of those weren't ever going to be a headache to maintain.
They probably didn't care. There's always a market for cheap devices. Why spend years and huge cash on research when you can sell them fash and cheap is the mentality.
There was a time, long long ago, when a manufacturer that wanted to build a reputable brand and stick around long enough to have it recognized....would make stuff that held up that brand.
Those names are far and few between because it's all about "first to market" these days. You would think with the speed "bad raps" get shared in this age of the Internet that manufacturers would realize they can't hide/deny/profit off bad product for very long before it catches up to them.
Right or wrong it's all about agile and the MVP "Minimum Viable Product" these days..
But honestly it's hard to see how small companies like Hubitat, Inc could even survive without doing so..
But in the case of smart home systems, quality devices with long battery lives weren’t a saving grace for Iris. Lowes still shut down the entire service (and stopped selling the branded devices made by a couple OEMs).
That was presumably a complex decision made by a large retail company that does a lot of other business not specific to smart home tech. But I think it’s unlikely Iris was making money hand over fist in the run up to that decision.
Several of the Iris devices were produced by Centralite, who filed for bankruptcy in 2019. The company also produced devices for Smartthings. They are still around now owned by the Ezlo/Vera group. I have a few Centralite water leak sensors. They use the older HA 1.2 Zigbee protocol. I try to purchase Zigbee 3.0 devices whenever they are available for future proofing. Hubitat still uses HA 1.2.
Download the Hubitat app
