Why is that? I actually have a phone (phones) that have a code base that I can build a ROM for without going broke.
While I can only build "old" ROMs, at least they let me get my feet wet.
In this case, it's the Pure Nexus Nougat series - for both the original Pixel (my Mom has one), and the old Galaxy Nexus that I used to own (it's still sitting on a shelf, in fact). While my Mom is, in fact, running Android 10 on hers, I may get one for myself as a straight testbed (I have a Pixel 3a that is my daily driver). Another thing that is attractive about the original Pixel is that refurbished Pixels are cheap (Mom paid barely $120USD for hers); they take nano-SIMs, and can run Android from 7 to 10 (yes - I said 10; Mom is running 10 on hers).
Another thing I found attractive about the Pure Nexus Project is that it was how I was introduced to the Pixel Launcher - it had everything I wanted in a launcher; to date, only one alternative has managed to equal it (and it's from the least likely of companies - Microsoft (Microsoft Launcher even does one thing Pixel Launcher has STILL not done; it supports non-smartphones - Microsoft Launcher can run on tablets).
I would LIKE to be able to build ROMs based on 9 or 10; the problem there is that it still requires too much CPU or RAM horsepower to go there at present. So I have to walk first; PureNexus is a ROM I'm famliar with (because I actually used to run it in my GNex days). I can actually get my feet wet - and on the cheap, too.
I would not mind company in keeping Pure Nexus for Marlin/Sailfish afloat - you can do it the same way I have, by firing up the Google-fu and digging up the GitHub for the Pure Nexus Project itself.