Cured villagers don't offer good discounts anymore.

I cured a zombie villager. I Had a good trade deal. I went and built something and came back and he was vanished. I had already got mending books and some emeralds from him. Anyway, I've cured 7 zombie villagers since and I don't get the discounts anymore. I only seen the good discounts for the first one I cured and than never again. This has made me not want to play anymore altogether. 
I built a really nice custom village to put a cute villager with good trades in each one and nothing works. Had I known I only had a very short window to trade with that cured villager and I could only do it right away. I would have taken full advantage of that. this has completely ruined minecraft for me and I won't be playing this game anymore until this is fixed. My entire world is ruined now and I did everything for nothing. this game just waists my time. I used to play many years ago but quit for the exact same types of things. I figured, the game would be a lot better nowadays but it's just the same and I'm highly disappointed. This game would be very good if it just worked like it's supposed to but it just doesn't. I was so pumped about this new world too. Should have known better. I stopped playing this game in the past for a reason and this is exactly it. You waist like a hundred hours building in a world for nothing just to have your entire plan and world ruined by something small and stupid like this.