Because we'd rather pay $325K for a home game v. a poor FCS team and chalk up a win over testing ourselves...
This actually makes sense, though. Let's do some math. We'll guess that travel expenses for a road game are $200,000, and expenses for a home game are $100,000. Let's also use $200,000 as an estimate of the home gate. Let's say you have a slot in your schedule for a game in 2015 and a game in 2016. You could schedule a home and home with, say, Marshall, or you could schedule a money game with Louisville, and a home game against Austin Peay.
Home-Home
Expenses -Road game - $200,000
Expenses -Home game - $100,000
Revenue - Road game - $0
Revenue - Home game - $200,000
Net - Loss of $100,000
Money Game+Austin Peay
Expenses - Road game - $200,000
Expenses - Home game - $100,000
Paid to Austin Peay - $325,000
Paid by Louisville - $850,000
Revenue Home game - $200,000
Net - Profit of $550,000
You could, of course, also do a third option - playing money games both times, and a 5 game home schedule.
Money Game+Money Game
Expenses - Road games - $200,000*2
Paid for money games - $850,000*2
Net - Profit of $1,300,000
How you mix these depends how badly you need the money. You also need to factor in that a home game supposedly adds about $500,000 or revenue to the Athens community, which closes some of the gap between $1,300,000 and the $550,000. Note also that as the home gate increases, the need for money games decreases. Let's say that they were able to sell 18,000 tickets to home games at $35 each. That makes the home gate $630,000. Now the numbers become:
Home-Home - $330,000 profit (+$500,000 to local business community)
Money-bought game - $980,000 profit (+500,000 to local business community)
Money+Money - $1,300,000