> what's in it for a project to deal with this extra architecture

You’d be surprised the number of companies who really want to run something on an obscure platform, and will pay $$$ to port stuff to it. Often the thing being ported isn’t even open source, it is some proprietary product, but that proprietary product has open source dependencies, and so someone ends up paid to port them to the obscure platform, to even try to upstream the port if the maintainers will take it.

Years ago, I knew of a small company which sold a CMS (I was going to work for them, but the job fell through when they couldn’t pay me enough); the CMS was proprietary, but it ran on an open source stack (LAMP). Some random customer said they’d only buy it if it was ported to IBM i (PASE, the AIX emulation environment), and they were willing to pay for the port, so it happened.

Later on, I worked for Oracle, and ended up on a project to port some ERP-related product to AIX - all because we had a big customer willing to pay millions for this product, but only if we made it run on AIX. And in the process I found an AIX-specific bug in JNA (the open source Java FFI library), and ended up helping the JNA developers to fix it