The only large publishers I could see Sony acquiring are Japanese ones, but arguably those publishers don't even need to be acquired. I could see Sony signing exclusivity deals with them, along the lines of what they have for Final Fantasy so that Microsoft is effectively starved of a bunch of games.
The key difference (the way I see it at least) is that publishers seem willing to make deals with Playstation, whereas none of the big publishers wanted to go exclusive on Xbox so Xbox's only option was to buy them out.
Plus, Sony acquiring publishers would only kill off the last bit of hope they could ever have of getting future acquisitions blocked. On the flipside, I can see your argument, which seems to be "Microsoft is going to buy everyone anyway so Sony may as well get in on the action", but Sony just hasn't got the money for it.
The problem Sony did was overshoot their dominance in the industry. Since 2013, everyone knows they blew by Xbox already, so them constantly doing deals trying to gimp MS's access to games (exclusive or timed deal) got so out of hand MS said fuck this and just bought people out knowing Sony would eventually get around to more and more deals.
Sony and Activision had been doing Diablo and COD deals since 2013, Sony has FIFA deals, and it was getting crazy where games like Forspoken (never mind it ended up a bad game) would be getting 2 year windows.
During the 360/PS3 days, each system had their share of exclusive games but that was due to regional interest Sony and Japanese games) or Xbox being more American/PC roots focused and getting some exclusives which also stemmed from being out a year earlier so in those early years of each console Xbox got Mass Effect. But as a whole there werent really any huge partnership deals aside from maybe some timed deals for DLC or preorder bonus differences.
Since the PS gaming division clearly makes more sales and profits than Xbox (regardless of whether MS discloses product line finances which they dont for Xbox) it's clear Sony would keep pushing for deals. And western style games like Bethesda (WRPGs) and Activision games (COD) being two key kinds of games Xbox gamers enjoy. So MS management said fuck this, Hey Nadella lets look into locking up these company's games so Sony doesn't get the opportunity to do more annual or 2 year deals etc... They already got COD partnership deals for two more years. They even did a Bethesda Deathloop deal etc...
If Sony and MS were battling each other like the 360/PS3 era when things were closer and neither side had so many significant partnership deals, IMO MS wouldnt be so trigger happy spending the bucks to buy. They'd just keep battling like that old era.
Its not just gaming. It any industry. When you shoot too far trying to dominate too much, you better be the biggest company in the category. Because if you arent, the one with the biggest wallet will eventually do ultra aggressive stuff to fight back fast and hard UNLESS they are the kind of company who would rather quit and disappear than fight the fight. In other industries, they'll fight more on price. And if companies all get into price wars the losers are ultimately the companies dumbing down the price which can be for years. My last company had the top two companies battling where prices were all dropping and each side would claim the other company did it first doing dirt cheap deals. I wasnt close enough in my role to know the industry data to see who started it first, but one of them did. It was either them or us and then the other company had to react back. At the end of the day it didn't even budge either company's market share. So it was really just a drain on costs for both of us. Customer loved it though because it went on for about 18-24 months.
In computing and tech it seems more like giant corps have so much money they will just buy each other out like it's chicken feed. IN gaming, it's not the kind of industry where if one company is losing, they react by making all games $20 cheaper hoping gamers come to them. Not sure why, but companies dont react like two companies battling on the price of soup. But MS is the one with the wallet.