It would make it too attractive to level your main to level 34+, which breaks game balance a bit.
I would use the sacrifice feature like this: once my 2h alt has a nice heirloomed 2h and i decide to go 2h with my main, i could retire my main, scarifice my 2h alt to absorb / transfer the heirloomed 2h to my main and make a 2h build on my main.
If you could just transfer items between alts and mains, there would be no reason to retire your main character anymore.