Cross compilation of entire distributions requires such distributions to be prepated for it. Which is not a case when you use OpenEmbedded/Yocto or Buildroot to build it. But it gets complicated with distributions which are built natively.
Fedora does not have a way to cross compile packages. The only cross compiler available in repositories is bare-metal one. You can use it to build firmware (EDK2, U-Boot) or Linux kernel. But nothing more.
Then there is the other problem: testing. What is a point of successful build if it does not work on target systems? Part of each Fedora build is running testsuite (if packaged software has any). You should not run it in QEMU so each cross-build would need to connect to target system, upload build artifacts and run tests. Overcomplicated.
Native builds allows to test is distribution ready for any kind of use. I use AArch64 desktop daily for almost a year now. But it is not "4core/16GB ram SBC" but rather "server-as-a-desktop" kind (80 cores, 128 GB ram, plenty of PCI-Express lanes). And I build software on, write blog posts, watch movies etc. And can emulate other Fedora architectures to do test builds.
Hardware architecture slow today, can be fast in the future. In 2013 building Qt4 for Fedora/AArch64 took days (we used software emulators). Now it takes 18 minutes.
Would you call Threadripper system "a normal build"? For many people they are normal builds because they need more computing power or more PCIe lanes than "normal user" desktop has.
On the other side you have those who pretend to use raspberry/pi 3 as "an Arm desktop" despite only 1GB of ram and 4 sluggish cores.
Fedora does not have a way to cross compile packages. The only cross compiler available in repositories is bare-metal one. You can use it to build firmware (EDK2, U-Boot) or Linux kernel. But nothing more.
Then there is the other problem: testing. What is a point of successful build if it does not work on target systems? Part of each Fedora build is running testsuite (if packaged software has any). You should not run it in QEMU so each cross-build would need to connect to target system, upload build artifacts and run tests. Overcomplicated.
Native builds allows to test is distribution ready for any kind of use. I use AArch64 desktop daily for almost a year now. But it is not "4core/16GB ram SBC" but rather "server-as-a-desktop" kind (80 cores, 128 GB ram, plenty of PCI-Express lanes). And I build software on, write blog posts, watch movies etc. And can emulate other Fedora architectures to do test builds.
Hardware architecture slow today, can be fast in the future. In 2013 building Qt4 for Fedora/AArch64 took days (we used software emulators). Now it takes 18 minutes.