Others addressed other aspects of the question, so I will focus on
If there such a positive response to the questions, why did the Soviet Union break up anyways?
First, the single question was phrased to consist of 4 parts:
- Do you want to preserve the Union?
- Do you want the union to be preserved as a Federation?
- Do you want the federal subjects to be equal and sovereign?
- Do you want equal right for persons of all ethnicities?
Note that 2 and 3 are mutually exclusive.
To vote, one had to cross out(!) the answer they did not like. So, if you vote "yes", you have to cross out "no".
So, it was basically "have you already stopped beating your wife every morning" situation.
Second, many republics did not hold the vote. IOW, saying that "the response was positive" is like saying that "4 wolves and a sheep decided democratically what's for dinner": the Russians voted to preserve their empire while (some of) their colonies tried not to participate in the vote.
NB: The apologists love to site the official statistics that every single republic voted "Yes". This might be true, because in most republics (Baltics, Transcaucasia, Ukraine) only a small fraction of population voted. To extend the analogy from the previous paragraph, "4 wolves and one sheep voted on dinner, while 6 more sheep ignored the vote".
This is, of course, disputed by the apologists who site the official Soviet statistics - the same statistics which brought us 100% participation rates for decades, and reached 146% recently.
Finally, Soviet Union did not break up (as in "disappear"). The Russian Empire lost some but not all colonies, but it is still there, and is now openly talking about gathering them back into the fold.