If he had to get only Alien Acidic, what would happen? Everyone would get his counterpick to wreck him in the next round.
Every character has another character as a bad MU, i.e.:
Mileena and Ermac against Sub Zero.
Alien against Jason and Leatherface.
Sub Zero against Tremor.
Scorpion and Takeda against almost everyone.
What would be Alien's counterpick?
@SonicFox5000 was smart enough to get Cassie and Erron Black as his secondary mains to get rid of his bad MUs.
Everyone started as any character being their first main, and then kept on with the secondary mains. This is why Tekken Master almost had the chance to beat him with Kotal Khan and D'Vorah.