Because we are talking about the companies’ behaviour today? MS is trying to buy one of the biggest publishers right now.
Secondly, most of those game studios already have a close relationship with Sony, they can be considered 2nd party, and mostly make PS games. Sony’s competitors aren’t losing out much.
P.S. Frankly, I don’t think Sony ever intended to be in the game development business - they are a hardware company. There is a pattern to the game developers they buy - almost all of them are “tech wiz” developers; i.e. optimisation gods while gameplay of their games are usually so-so. The raison d'être of their acquired studios are to showcase the power of their hardware and coincidently provide development tool chain feedback as well as development knowledge which Sony’s “ICE team” will then share with other developers, not compete with their 3rd party developers.
That said this might have change in recent years as exclusives become a differentiator for their console.
Speaking about the origin of Sony PlayStation divison (Sony Computer Entertainment), it was derived from Sony Music. Its origin was a content company than a hardware company.
The PlayStation all started with Ken Kutaragi who worked in Sony’s digital research labs. It started as the “Play Station” a CD addon for the SNES. But due to contract disputes Sony got dumped for Philips in a very public fashion - probably Nintendo’s biggest mistake ever. Sony went ahead on its own and created the “PlayStation” (aka PS1 today) and the rest is history.
