The tools subpackage depends on libblockdev.so.2()(64bit) on all architectures.

$ rpm -q --requires /home/vtrefny/rhpkg/libblockdev/results_libblockdev/2.28/1.el8/libblockdev-tools-2.28-1.el8.x86_64.rpm
libbd_utils.so.2()(64bit)
libblockdev = 2.28-1.el8
...

This happens only on RHEL 8 where the dependency is automatically added. On RHEL 9 or when doing a local build on Fedora the dependency is not added (with the same SRPM).

I am marking this as a low priority because the libblockdev-tools package is not shipped on RHEL 8.