So what? What makes you think that just because someone is ethnic Russian that they'd prefer to be part of Russia rather than Ukraine? Zelensky himself is of Russian ancestry.
When the issue of Ukraine becoming independent was put to voters in 1991, 55% of voters in the Crimea voted for independence rather than remaining with Russia. Percentages varied across Ukraine -- as you'd expect in a legit election -- and there were no claims that the election was rigged. Accepted as fair by Russia itself.
So in terms of respecting "democracy" and "self-determination", the only ones who aren't respecting it are the Russians, who are trying to annex by force areas that freely voted to leave Russia and become part of Ukraine. And which Russia itself agreed in 1994 would forever remain part of Ukraine.
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In 2010, polling in Crimea showed that support for joining Russia was significantly lower than the overwhelming majorities reported in the 2014 referendum. According to multiple reputable sources:
In 2010, about 33% of Crimeans supported joining Russia.
By 2011, this figure remained around 33%, and by 2012 it had dropped to less than 25%.
In 2013, support for joining Russia was 23% according to a poll cited in Wikipedia.
A poll conducted by the Kiev International Institute of Sociology in February 2014, just before the Russian intervention, found that 41% of Crimeans wanted Ukraine and Russia to merge into one state, though this may have been an overestimate compared to earlier years.
In summary, in 2010, roughly one-third (about 33%) of Crimeans wanted to be part of Russia, with support declining to about 23% by 2013.