Companies are not made of 100% engineers. Production costs are only part of recurring expenses in a business. At the very minimum you have to pay an executive team, a marketing team, a network/security team, a legal team, an accounting team... these guys don't work for free, and want to be paid every year at worst - more often, every month. Even if each "team" is one person in your garage, you have to pay them. And when you scale up, now you have investors to service, and they also would very much like to get regular dividends from their investment (or see constant growth in the value of their share).
Note: I'm not defending the practice (if you dig in my comment history, you'll see pretty incendiary stuff against SaaS abuse very recently), I'm just saying that it's what business naturally tends like - in the same way it naturally tends towards paying people as little as possible, exploiting them, etc etc. This is what the market becomes when left to its own devices. If we don't like it, we need to proactively intervene in law.
