Probably because Kotick is 59 years old and wants to retire soon, plus an acquisition would help in terms of PR to get rid of the controversy while helping the ABK investors (as Kotick, who is confirmed to continue as CEO) to earn a ton of money.
Plus CoD was on a sales decline, Vanguard didn't perform as good as desired even if they had all their teams, WoW has their own things with FFXIV and others taking over the MMORPG lead, Blizzard development controversies with Overwatch or Diablo, key staff leaving, workers causing controversies with harassment stuff, random layoffs and other isues, etc.
So it was a key moment for an acquisition for them, since whoever bought it would have to handle the shit show circus pretty likely under a new management. It's a very specific moment where it was good for ABK to sell, in normal conditions they wouldn't be interested on selling.
Traditionally companies want to sell because they are in awful financial conditions and to sell is their only option to go bankrupt, because they are stuck and can't grow if it isn't merging with someone or selling the company to someone who can help them in other key areas where they want to grow or something like that.
EA, Take 2, Square Enix, Ubisoft, Bandai Namco, Epic, Valve, Konami, Sega or Capcom aren't in this situation so very likely they won't want to sell. And well, the Japanese government doesn't allow to sell Nintendo or Sony to foreigners.