A: The Trump administration is in favour of big business to the point where they are going to let AT&T and Time Warner merge 99% intact despite saying before the election it would never be allowed.
B: A combined Hasbro and Mattel will still have plenty of competition because of Bandai Namco, Jakks Pacific, McFarlane Toys, Takara Tomy, etc.
In the case of Microsoft in the 90s it really was the case that 99 point something percent of the market was made up by Microsoft and Apple combined so seeing Apple go would have been effectively a 100% monopoly.