No one knows when based on technology or the economy, but there is a fairly high probability that the tower or billboard will be removed or relocated to an alternate location in the future. This can be based on technology or traffic patterns and most leases allow for such cancellations.
Of course, they say the turtle wins the race. But many times, people are not willing to wait 10 or 20 years for what they can have today. Even if it is a discount of the total amount, many would rather have the funds today.
High-interest debt, such as credit card debt, can quickly lead to low credit scores and impede future purchases.