And yet Amazon which is 300% bigger can buy iRobot with no issues. I’m so confused by the weird random things the EU and US block wrt to mergers and yet they don’t block massive obvious ones it seems.

It's not about size it's about influence

Influence? Amazon and Bezos control a huge portion of retail, the internet (aws), the entertainment industry (prime, MGM), gaming (twitch), Washington post… I could go on… they are hugely more influential than anything meta is doing.

AAG and Microsoft are incredibly influential and powerful.