But, why, in any case? Voting is also a right extended only to a portion of the residents of a country (I can't vote in the US and I live here). Protest is a mechanism for sending a direct message, and it is extended to everyone in the country. Voting is a mechanism for choosing between the candidates on offer, protesting is a mechanism for sending a message to any target. Voting gives power to your choice, protesting tells them what to do with the power they've been given.
The objective of a protest is not to create a world where Trump is not inaugurated, but to set Trump and other politicians on notice that they govern only by the most tenuous of margins, that their words and actions have alienated the rest of the population, and that to the extent that one of the president's biggest tools is political capital, he starts with relatively little. None of this depends on whether Russia tampered or didn't and whether the tampering was crucial for his election or not.