Doesn't this happen somehow? it's just hard technically, I'm sure we can improve the UX
+ Android
+ Windows
Android is fully open source, oonly the play store is controlled by Google. China already has a lot of alternatives (and have a look at Huawei on how well that block worked).
Windows would put hurt a bit, yes, but cracked versions of it are not a rarity. Additionally, there's always Linux. So unless MS remote-wipes their machines (and kill themselves by doing so), it would probably not hurt either.
And if the country is smaller, like Nigeria, China will be happy to offer their help for a bit of political influence.
And why not to let them? Half the kingdom for a privilege to kill somebody's Facebook page? A very good trade.
Dictators are even more well aware than democracies what opening the door to Beijing means. They will rather not to.
Honest question. These companies are large, but they don't have too much power in these countries. Especially China has a lot of internal alternatives (Aliexpress cloud and Baidu for example), so external pressure will really only help them. Case in point: Huawei's Playstore ban - this would probably have killed the phone division of a western country. Then there's the problem of biting the (kid's) hand that builds your hardware and/or servers and the one that pays your bill (AWS customers are not going to be happy when their Chinese customers are blocked).
Irrespective of the discussion on whether the tech giants taking such massive political influence is a good thing, I simply don't see how they could.