Except, it has been shown time and again that as technology advances, food gets cheaper and cheaper due to developments in agriculture, storage and preservation, and transportation. If they have the technology to colonize mars and jump between stars, they have the technology to harvest, preserve, and transport beef with ease.

Thinking towards kleinbl00's idea that maybe beef is a rarity due to some unknown factor or another, I'd have to kabosh that idea as well. For one, beef is a staple meat for many, many cultures. If they're able to colonize mars and travel between the stars, chances are they wouldn't have any trouble making sure that the both the genetic stock and the environment needed for raising beef stays viable. Additionally, since their first mission was in Mexico of all places, they were in close proximity to earth so transportation wasn't an issue. Lastly, the way they non-nonchalantly talk about beef like it's an easily expected every day meal, which means it's common and affordable for two space goons like them, instead of some rare delicacy where they have to go to some clandestine restaurant and pay the future equivalent of $10,000 for a plate of forbidden bush meat.

Easiest explanation? They're bad budgeters and their misery is their own doing.