That's just bad business. MS paid a fortune for the Minecraft IP. Not the expertise at Mojang, because that's not something that can be owned in perpetuity. The situation with Insomniac is the reverse, their real value is their ability to work with other people's IP. Insomniac don't own Spiderman, Ratchet & Clank, Spyro, Resistance. Everything they are best known for is owned by other parties.
They also run their own tech, which has limited application in terms of corporate synergy. You can't just cobble engines together from disparate sources, intreroparability and consistency of toolchain and interface are vital for productivity. So basically paying money for technology that's only going to apply at the sites where it is initially situated dilutes its value.
You need to consider "buying" a company is just a one-off payment for transfer of ownership, its the START of expenditure, not the end, and that investment needs to be recouped. Hiring that same company for development, whilst retaining IP and publishing rights, is far more cost effective and accomplishes the same thing.
If throwing $500m away as a one-off sunk-cost to elevate your business is a viable strategy, spending it on buying a studio is far from the top of the list of smart moves.