Because that warlock card is old and outdated. Powercreep is real, and reprints can happen too.
Here is an example: My favorite card Electra Stormsurge got now reprinted into druid spell 2 mana (Solar Eclipse) that does the same thing in cheaper cost. Is it unfair that druid card is better than that legendary shaman minion? Sure it is. But Electra is outdated too, so it's reasonable.