In the alternative. They could have sent it to an wild animal rescue center and be given to someone who had a herd of buffalo. It is very common for female wild animals to adopt the young of others. In fact there was a case where a wild cheetah adopted a wild antelope, going so far as to protect it against other cheetahs. For an alternative view, sometimes mothers cast off their off spring when they sense something is wrong with their calf, e.g. malformed.
In the old days ( earlier than 1980) some park ranger would have taken it home and their kid would have had a pet. In the 1970s, someone made a short 15 minute film about all of the pets that park rangers had. The film show a complete menagerie of wild pets, to include buffalo and elk (no grizzlies though).
In the alternative. They could have sent it to an wild animal rescue center and be given to someone who had a herd of buffalo. Most anything is possible with enough money.
A bison calf appears to be worth about $2500 to $3500.
It was probably the extensive bureaucratic rules which killed it.