Why does Pokemon use animals? Why only discover drowsees origin? Why is Pokemon so fun? Will they make a better Pokemon game?
1. Not only animals, but pretty much anything they can personify; myths, legends, food, ghost items, weapons, rubbish, ect. It's pretty much how Pokemon's been from the outset and the reason being was to recapture Satoshi Tajiri's childhood of catching bugs and trading them with the local bug collectors which when you take to a game concept doesn't sound really appealing. It's incidentally also why the games utilise trading.
2. Drowzee's origin is somewhat frayed and besides the person in question might be interested in what inspired that Pokemon. Even then sometimes people are just curious about Pokemon origins be it ones they aren't familiar with or ones they like.
3. This one's not quite as easy to answer alone so I'll put a video which explains why it's popular and enjoyable.
...But essentially like any form of entertainment and enjoyment, it appeals to and makes the target audience happy. "Fun" in this case is subjective to what the audience thinks is enjoyable and fun to them. Some people like Zelda or Mario or Halo. Some people like to read a book, others like to watch TV, some people even get enjoyment simply out of the newspaper crossword. Video games are special like that since it allows a player to actively participate and experience a fictional fantasy, which is something movies and books and TV lacks. To Pokemon fans they enjoy it because it's appealing to them and what they consider "fun."
4. Again, "better" is subjective to what you consider is better. Unless you're talking about the newest generation, in which case I would assume 1/5-2 years from now at least.