The reason behind this is actually quite simple: it's easier to focus on boys than the entire population. Let me explain.

Companies often divide their market into many many divisions so that, they are able to focus on each group individually, rather than trying to sell one product to everyone. This is known as Market Segmentation. The easiest segmentation here is in terms of gender. Which is why, you see the same shampoo with two different names & prices; one for male and another for female.

Back in 1983, when the gaming industry took a massive hit, going from over 3 Billion Dollars to around 10 million by 1985. During this time, most gaming companies tried to shift from electronics to the toy industry.

Here, one very specific company thought it would be a great idea to segment the video game market and create a product catered specifically towards male or female gamers. And, they just happened to choose the former. :))

During this time, many games were made catered towards that audience and the unavailability of games "made for girls" was the key reason why many girls turned down gaming and the industry decided that the market for gaming in girls is declining.

Thus, by segmenting the market, this company was able to bring gaming back to a respectable position while also setting the standard for all the games to come after it.

The company's name is Nintendo and the product I'm referring to is their very first hand-held console released in 1989 literally named as "Game BOY".

Funny how a good marketing strategy can influence our thoughts and beliefs.