I do wonder what Microsoft's game plan is here but I'm seeing a few possible reasons.
1. Set themselves up to acquire a Japanese publisher - I think this is the least likely because Activision-Blizzard will keep them busy for a couple of years, I don't really think that is on their mind yet.
2. Put pressure onto Sony in this newly defined "High-Performance Console Market" - Essentially making it harder for Sony to argue that Microsoft acquisitions will cause an SLC which is how a few regulators, such as the CMA, decide on whether to approve a deal or not.
3. Put pressure onto the FTC in a roundabout way - Essentially slyly pointing out how much dominance that Sony has in Japan and that Japan "protects" that so the Activision-Blizzard deal should go through in America, essentially along the lines of "you should look after your own too"
I think a combination of 2/3 are likely. Especially because we don't know if Japan agrees with this market definition but we know FTC does and we know Sony does so you can use their words against them with other regulators. The FTC is the only one remaining with a Console argument.
These Politicians are specifically talking about Trade Agreements though so I think a few people are losing their minds over nothing, a Politician trying to improve Trade Agreements is like the most common thing ever, it's no different to when any country complains about if they feel their companies are disadvantage in any other sector in another country they have trade deals with.
I don't think Microsoft is expecting Japan to stop Sony from making timed exclusives, Lol.
Whether people like it or not, this merger isn't against any US Law, it doesn't represent an SLC in Console Gaming in both Europe and UK and it doesn't give Microsoft any significant market share dominance, another reason to block the deal. However, Microsoft is using Sony's market share dominance against them in this newly defined market in order to grow their own business, which is a reasonable tactic.
It was Sony's fault that this newly defined console market was even created, it was Microsoft who tried to include Nintendo at first. Now it exists and I don't like that it exists but that is FTC's fault and if EC/CMA also support it then well, tough luck for Sony because it paints a picture of Sony dominance across multiple major markets.
Pointing out that Microsoft is being destroyed in dozens of markets just backs their point up even more than the ABK acquisition should be allowed to go through, Lol. The definition is stupid but it exists and it exists because major regulators agree it exists and Sony encouraged it.
People are losing their dang minds over this 
Regulators & Politicians are getting a taste of the "Gamer Console Wars" between those who accuse the regulators of being corrupt over approving the deal to witch hunting against Politicians over straight up lies, caught in the crossfire between Xbox and PlayStation fanboys It's nasty, it's not a good look for the industry, I hope this is over soon.
