Not quite as easy as you suggest. The kinds of measures which calm down the Poles tend to be seen by the Russians as a provocation, most notably NATO membership. Washington could try to pressure the Poles to avoid silly provocative symbolic stuff of the sort the Twins like to engage in, however, they have absolutely zero ability to do the same on the Russian side.  Plus it's not always clear if Moscow is able to distinguish between hardline governments and the moderate ones who are interested in better relations.

And while you are correct to say that the knowledge of Soviet atrocities is easily available, it isn't all that well known - e.g. very few Westerners are aware that the Soviet occupation of Eastern Poland was just as brutal as the Nazi occupation was for non-Jews. (Rather ironically, if the folks currently running the show in Moscow had had their way back in the nineties, we'd still be thinking that it was more deadly, but the brief access to NKVD archives showed that to be incorrect)

On the Estonian side, Washington also has the problem that it has zero influence on Moscow. It could try to pressure the Estonians to do things like keep the monument, but that's difficult to accomplish without apologies for both occupations and the atrocities they involved.

In general I'd say that the Russians would be well advised to look at the approach the Poles have taken in their relations with Ukraine. That has involved lots of apologies, long drawn out negotiations over Polish national symbols in Ukraine and how exactly they can be modified in such a way that satisfies Ukrainian sensitivities while keeping them in place, and ignoring things that the Russians would treat as provocations (e.g. the honoring of Ukrainian fascist militias involved in massacring Poles in what is now Western Ukraine). It's a policy that has been followed consistently by not just moderate governments, but also hardline nationalist ones who ignore the screams of outrage that regularly emanate from their own ranks. If a former occupying power wants to have good relations with its ex-victims, that's the way they need to operate.