Structure count vastly different (noob question)

Sorry all, I'm new to the game but appreciate the difficulty and learning curve. I've been trying to beat the employee difficulty practice game and am having a tough time. I'm noticing that at the end the structure count tends to be me around 25, and often one of the computer players will have 50 or 60 structures. Is this because they bought a ton of auctions and parcels from the black market?