I think IP laws and patent wars are a lot more salient when it comes to hardware (like Apple, Samsung, Motorola, etc), less so for those 3 examples.
And in any case, many tech giants exist around natural monopolies, either in network effects, either obvious ones, or those from two sided marketplaces or simply economies of scale.
Yes, network effect is a huge part of the problem. So much in tech requires user adoption, and typically users won't adopt until others adopt, thus creating chicken and egg problem. Overcoming the network effect is extremely difficult, as we've seen from competing platforms trying to unseat facebook and twitter (tho network effect is not limited to social networks, but they are the most obvious examples)
In fact, many people in China attributes Tencent's growth to its shameless copying of other people and companies' work and products. If that kind of view is true, than China's monopoly comes out because of lack of IP protection.