Actually there is an old industry reasoning behind this, and it dates back to the inception of the arcade game and their popularity in the 1970s. At this point, most games were designed entirely by a single individual, so if a game proved to be popular, it would mean that a lone person's idea had proven fruitful and valuable, and their other ideas might take off as well.
As the early arcade heyday was fiercely competitive, a lot of companies from a variety of industries tried to break in and beign producing their own machines. To bolster their game development departments, or in cases of small companies looking to one-up the competition, they would often try to hire talented individuals out from under other companies. To prevent this, companies like Atari specifically forbade their employees from putting their names on the games they created, so they could keep their employees when other companies were trying to hire them out from under them. Culture also played into this, as many game company heads believed designing popular games were easy work, so game developers shouldn't be excited over credit or receives bonuses when they were successful. This became an industry-wide practice, with a couple of interesting historical firsts spawning from this: the first Easter Egg was a hidden credit title giving the name of the developer, and the first independent game developer(Activision) was formed by Atari employees who wanted credit for their work.
When Activision was formed in 1979 by David Crane, Alan Miller, and Bob Whitehead(with Larry Kaplan joining them a short time later), along with former music industry executive Jim Levy, they specifically founded it to give focus to each designer, and to oppose Atari CEO Ray Kassar's statement that "anyone can do a cartridge." Atari sued, and Activision beat them in court, opening the floodgates for any company interested in trying to make money on the new and potentially lucrative video game market, such as the Connecticut Leather Company, Quaker Oats, and so on. And the culture changed at Activision, first with Larry Kaplan leaving in 1982, then the market crash in 1983, then Miller and Whitehead leaving in 1984, then Levy and Crane leaving in 1986.
To prevent these kinds of uprisals, but still in an attempt to keep their best designers, many Japanese companies began letting their employees put special nicknames in credit sequences for games. Sometimes these nicknames would remain consistent across the industry, such as Hyper Shinchan(also known as Shinchan or Shinchan-SSS), who first used the nickname at SNK but then later at Hudson and Capcom. The names in Bone's Phantasy Star example are great renditions, though employees still weren't happy and found other ways of slipping these names in, such as Akira Nishitani slipping his nickname "NIN NIN" into Street Fighter 2 high scores and this particular background.
In general, game devs aren't treated well(companies like Electronic Arts are rated some of the worst in the United States), and games have moved away from the single individual and into massive teams. And sure, games can be hugely profitable(can be, but most aren't. Only an estimated 1 in 4 turn a profit, and these are often small games that are being used to fund much bigger projects with massive teams costing millions or even tens of millions to design, produce, and distribute, which is how a game like Tomb Raider can rake in millions and still not make up the money that was spent on it), but the industry is highly competitive, and many devs worry that putting out their employees names will make rival companies target them.
Also, tech work is cyclical, and many of the designers on games will come and go on a contractual basis, depending on the needs of the company. When they do work, they will usually work full time or beyond, depending on whether "crunch time" is in effect. And there are a lot of people who want to make games, so finding replacements is actually pretty easy at this point, as generally no one individual is making all decisions in the process(unless it is a big name person with clout who serves as a brand or a really small dev team, like Charlie "Flayra" Cleveland and the Natural Selection series).
)