I will continue to believe that the bite of '87 was not a literal chomp out of a person's brain until we are given conclusive proof. I will continue to insist that it was an extreme blow to the company's finances. And I will present my case for the unfamiliar faces.
1. In FNaF2, it's noted that the company spent a "fortune" on the toy animatronics, and pointed out shortly afterwards and on later nights that their programming has been tampered with or is incomplete, such as no proper night mode or "they just... stared." This would naturally cause large safety concerns, giving cause for the company to close the location, discontinue the toy models, and squander their costly investment before the week is over.
2. Continuing with FNaF2, in the newspapers, the location is having a grand opening. This means it's been relatively recently bought and refurnished, and it is a big building. Considering the costs of opening a larger restaurant are about $300,000 (US dollars) in 2017, using an inflation calculator, we can find that the cost of opening the location in 1987 would be about $139,127.59.
This is no small amount of money, even by today's standards, and that's not counting the costs for the animatronics, meaning it cost them even more to start the location. And thanks to the vent situation, we know they were already cutting corners on costs, which means this is something that needed to pan out. When it didn't work out, the company clearly took a financial hit.
3. Moving onto the FNaF1 location, our first hint is our limited resources. A limited amount of electricity means that the company put a cap on it, likely to reduce costs. In the 1987 location, the electricity was limitless, except for the flashlight.
The location is also significantly smaller, and as implied in the newspaper at the end of FNaF2, is a previous location. This would cost significantly less to move into, since it's already essentially set up.
4. As for the Phone Guy's frontal lobe remark, which sounds pretty damning, it's important to remember that the frontal lobe is where we make many of our conscious decisions, including finances and monetary investments. "Amazing how you can survive without a frontal lobe" could be an insult towards upper management for their poor investment decisions, which he'd know about, since he worked at the 1987 and older locations.
Some may claim that FNaF4 depicts the bite, but this simply isn't true. First off, the child did not survive for an extended period of time. Only for a week, if that.
Also, in Sister Location, if you input 1983 on the keypad in the office for the false ending, you see the FNaF4 house, further implying that it happened in '83, not in '87.
Thank you, whoever read this.