Why is tencent constantly allowed to buy up every company slowly and become massive but Microsoft has to face a massive battle when purchasing Activision/Blizzard
The first argument is not true. Tencent is one of the top 3 largest video game publisher in the world both by net worth and by revenue. It may not have its own console but it's definitely on par with Microsoft and Sony when it comes to the gaming market.
That said, I'm not a fan of @Whiskeyomega 's framing "but Microsoft has to face a massive battle when purchasing Activision/Blizzard" as if Microsoft is a poor little oppressed mom and pop shop, that if another megacorp behemoth gets to consolidate the market, it should too.
It would be better if Microsoft didn't get ActiBlizz, especially considering that it alone is another top 10 publisher with many studios under its umbrela. It would also be better if Tencent didn't get to acquire studio after studio, which should be brought up to the attention of European Union regulators.