The reasoning is obvious, and "plausible deniability" is not enough to give Google charity. The more difficult you make it to block ads, the more impressions, and the more money made. Yet you believe people should be "charitable" to the same company that can't hire the manpower to defend their own users against bad faith DCMA takedown notices. Because they ran the analysis, and it wasn't worth the cost.
Best case scenario, Chromium loses market share, implements the parts removed from V2, Google likely kicks the can down the road to Manifest V4.
There's no reason to believe companies deserve charitability. Companies are systems designed to extract maximum value, and when the world around that system changes, the system adjusts itself. It's not the systems fault for trying to get more value, it's our fault for letting them.
Eventually, there will be an overstep that make enough capable people mad, and those people will get together and make/mod something better.
Sure, it doesn't rule out google was secretly intending on doing it, only internal memos or whatever can prove that definitively. But at the same time, to immediately conclude that google was "abusing its market position", you would have to be maximally uncharitable to google. That's a sad way to see the world. Take for instance, the flak that google got for banning third party cookies. If this is done by anyone else (eg. Firefox), this would be seen as a good thing. However, cynics have opposed this on the basis that such change would disadvantage third party ad networks more than google, thus google was "abusing its market position to their own benefit" and therefore the change was bad.