Genuinely want to know why you’re “not allowed an opinion” if you didn’t vote ?

Keep seeing everywhere “you’re not allowed an opinion on what’s happening then” as a reply to people saying they don’t want to vote and I could just be a silly sausage but just why? I feel like whoever you vote for, you have a valid opinion on the absolute bs we’re constantly put through bc you live here, no? Don’t understand why voting has a deal in it.