Why do so many people sneak into gyms?

Went to CityFitness tonight outside of staffed hours for a workout. Was on the treadmill by the door and noticed at least 6 people sneaking their friend in within the 45 minutes I was there.

Most of these people had expensive workout gear on, nice shoes and brand name wireless headphones on.

The base membership at CF is $7.20 per week. Are people really that selfish that paying $7 dollars to go to a nice clean gym with dozens of good machines, free weights and facilities (less than $1 a workout if you go everyday) that unfeasible?

Interested to hear the other side of this.