It says right there in the article. BASIC had books like "101 computer games" published for it. It had already made Bill Gates a minor celebrity. It already had the most mindshare in his target market.
> "The key to games was BASIC. Bill Gates was unknown except in the electronics hobby world. Everyone in our club knew that he'd written BASIC for the Intel microprocessor. I sniffed the wind and knew that the key to making my computer good (popular) was to include a high-level language and that it had to be BASIC. Engineers programming in FORTRAN were not going to be what would start a home computer revolution."
> "The key to games was BASIC. Bill Gates was unknown except in the electronics hobby world. Everyone in our club knew that he'd written BASIC for the Intel microprocessor. I sniffed the wind and knew that the key to making my computer good (popular) was to include a high-level language and that it had to be BASIC. Engineers programming in FORTRAN were not going to be what would start a home computer revolution."