Questions & Answers about Mi voto cuenta.
Because yo means I, and that is not the subject of this sentence.
The subject here is mi voto = my vote.
So the verb has to agree with voto, which is third person singular:
- mi voto cuenta = my vote counts
If you said yo, the verb would need to match yo:
- yo cuento = I count / I am counting
- yo voto = I vote
So Yo voto cuenta is not grammatically correct.