Basically, at this point MS already had an understanding what games are a great driver for selling both the OS and apps, but the game market itself was too small to bother with more than being a publisher:

>> In the United States, Age of Empires debuted at #7 on PC Data's computer game sales rankings for October 1997.[36] It secured places eighth and 13th the following two months, respectively.[37][38] By the end of 1997, Age of Empires totaled sales in the country above 178,000 units, for revenues in excess of $8 million. This performance made it the United States' most successful real-time strategy game during late 1997: a writer for PC Gamer US noted that its sales surpassed the combined totals of rivals Total Annihilation and Dark Reign over the same period, and were over four times greater than those of Myth: The Fallen Lords.[39]

Sure, AoE was a great success eventually ($120M revenue, by 2000) but it was a hit which surpassed many, many other games and but it took a lot of time; while this was still a summer of '97.