The main theme is often about different forms of love. It could be romantic love, like the deep connection between two characters. For example, in some short films, two characters might go through various challenges together and in the process, their love for each other grows stronger. It can also show platonic love, such as the friendship between characters that is so strong it resembles love. And sometimes it might explore the love within a family, the bond between parents and children or siblings.
Often, there are two main characters who are in love or about to fall in love. They could be different species, like a boy and a magical creature. This shows that love can transcend boundaries. There are also sometimes side characters who support or oppose the main characters' love, like friends who encourage them or villains who try to break them apart.
Not sure. I haven't come across 'Joy Story' being identified as a Pixar short. Maybe it's a relatively new or less popular one that I'm not familiar with.
It's possible that the team at Pixar felt that the full-length Toy Story 4 told the story completely and didn't require a short to enhance it. Or perhaps they wanted to save their creative energy for future installments or different projects altogether.
It could be that the story of Toy Story 4 didn't lend itself well to a separate short. Or perhaps Pixar had other projects in the pipeline that took priority.
One of the most popular Pixar short stories is 'Bao'. It tells a very touching story about a mother and a dumpling that comes to life. The unique cultural elements and the deep emotional connection between the characters make it extremely popular.