Depends (a) how many maintainers you have, and (b) how many "consumers" you have.
Can you imagine how hard it would be to get SUSE, RH, Ubuntu, and any other distros with LTS's, all to pick the same kernel for their releases in approximately the same time frame?
And actually, I think the kernel team only have ONE serious branch, not several. There are several development branches, that all feed into the "one true branch", that then leaves a trail of stable and semi-stable branches in its wake. And each branch has its own raison d'etre.