Most boards have some ecosystem to rely on. Either mainline support, some community organized either independently around a particular SoC manufacturer (like linux-sunxi), or around a board manufacturer (Radxa, Pine64, ...), etc.
You're rarely on your own. And even if you are, it's much easier when you have an actual detailed SoC documentation, board schematics, and when things are not some weird ad-hoc thing, but something fairly standard like U-Boot, that you already know and can re-use the knowledge of on any other board, without any vendor lock-in, etc. And when the docs are not some completely ridiculous thing that Rpi was known for years ago.
I'll put it this way, I have a project I'm considering where both a Milk V Duo and a pie zero would probably do fine. But if I follow the raspberry pi example, there's dozens upon dozens of examples for me to look at. If I use the Milk V Duo I'm going to have to figure out that stuff by myself.
The libraries for a pi hat might only exist for the pi for example. I guess I could write my own library though.
Yeah, there's a difference in available public resources between a chip nobody knew anything about just 6 months ago and is just getting upstreamed to Linux in the current release cycle, and BCM2835 from Rpi Zero which has been around for 11 years.
Are you serious? :) At least compare with something like Allwinner H3/A10/... which had similar lifetime.
At the end of the day I know a raspberry pi chip will be supported 6 months from now. I don't know about a new RISC V chip that literally just came out.
You're rarely on your own. And even if you are, it's much easier when you have an actual detailed SoC documentation, board schematics, and when things are not some weird ad-hoc thing, but something fairly standard like U-Boot, that you already know and can re-use the knowledge of on any other board, without any vendor lock-in, etc. And when the docs are not some completely ridiculous thing that Rpi was known for years ago.