The Yalkut on our parsha writes that when Bnei Yisrael came to accept the Torah, the nations of the world jealously asked why we deserve to come closer to Hashem then they did. Hashem replied to them, "Bring me the records of your yichus... like Bnei Yisrael have." This, says the Yalkut, is why the Torah juxtaposes the count of Bnei Yisrael in our parsha, which entailed each person tracing his lineage "l'mishpichosam l'beis avosam," with the pasuk, "Eileh hamitzvos asher tzivah Hashem... b'har Sinai," which concludes sefer Vayika.
Why should the nations complain? Chazal tell us that Hashem offered them the Torah before giving it to us and they turned him down. They had their chance!
The answer is that the nations complained because the scales were tipped in our favor. When Hashem offered us the Torah, it was an offer we couldn't refuse -- "kafah aleiham har k'gigis." He did not do the same for any other nation.
This is the point the Yalkut comes to resolve.
The halacha (C.M. 205:12) tells us that if someone is coerced to sell something, the sale is valid, but a purchase made under duress has no validity. Chasam Sofer (B"B 48) explains that a seller merely has to relinquish ownership for someone else to step in; a buyer has to establish a new claim to the item, which is harder to do.
R' Noson Gestetner in his sefer on chumash explains that even if Hashem were to hold a mountain above the nations and coerce them to accept the Torah, their acceptance would not be valid -- a kinyan cannot be made under duress. However, when it came to Klal Yisrael, accepting the Torah, it was not a new kinyan -- it was a yerusha that we had form our Avos and previous generations.
"Bring me your yichus records," Hashem told the nations. You are not the bnei Avraham, Yitzchak, and Ya'akov. You cannot claim the Torah as a yerusha, and will not give it over as a morasha, as one generation does not connect to the previous one. Therefore, kaga aleihem had k'gigis would not help you absent a real desire to receive the Torah.
Nice pilpul, but I think you can say perhaps a simpler pshat as well. The nations want closeness to Hashem. Hashem's answer is that closeness to Him is midah k'neged midah contingent on one thing: our closeness to each other. "L'mishpichosam l'beis avosam" -- every member of Klal Yisrael connects to his family, to his sheivet, ultimately to the tzibur as a whole. We connect with each other, therefore, we can connect to Hashem. Only Klal Yisrael has this virtue.