The reason i believe Microsoft Basic became popular across multiple platforms is because nobody else sold their BASIC to other hardware vendors.

In those days the money was in hardware which cost a lot, and software was thrown in. It wouldnt make sense for IBM to sell their BASIC to another hardware vendor.

Microsoft was different, they would sell their languages to anyone and they did. Can anyone actually name a competitor in those early days ?

Even Apple didnt sell their own Woz written basic to other 6502 vendors, C= had to buy Microsoft Basic.