The Mekor Baruch* writes," Rosh Hashana we end the Bracha with Mekadesh Yisroel Veyom Hazikaron and on Yom Kippur we end the Bracha Veyom Hakipurim. In both cases we specify the name of the Yom Tov.
Whereas by the Sholosh Regolim we end the Bracha with Vehazmanim instead of being specific to end with the name of the Yom Tov (Mekadesh Yisroel Vechag Haposach etc.)
A second problem is, It would have been more appropriate to say Umoadim, the Loshon in the Torah, instead of Veshazmanim.
The Mekor Baruch suggests, when the Gemoro says to end the Bracha with Vehazemanim the Gemoro didn't mean to end the Bracha with the word VeHzmanim.
The Gomoro meant to fill in the blank. Each Yom Tov you need to specify the name of the Yom Tov. (Mekadesh Yisroel Vechag Haposach, Vechag Hashovuos, Vechag Hasukos .)
He writes he told this to his father (The Aruch Hashulchan) who agreed that it makes sense. The Aruch Hashulchan said, even though it sounds true, since Klall Yisroel learned Pshat in the Gemoro, the word Vehazmanim is the actual word to say and Klall Yisroel has been doing so for the past thousand years, therefore we can’t change the Nusach.
*R. Baruch Epstein (Torah Temimah