In the ending to Toy Story 4:
- Woody gives up his badge, symbolizing that he's no longer in charge of everyone's safety, and he's ready to retire
- Woody no longer has his voice box and is therefor now nothing but a doll
- It's revealed that Woody is old as shit and heavily implied that no kid would be into him anymore
- All the toys part ways except for Bo Peep and Woody
There's literally nothing they could do to expand upon their stories at this point. The journey is over. They went from being scared of a new world in Toy Story 1 when Buzz first came to Andy's room, to really coming to terms with the fact they're toys in Toy Story 2, to coming to terms with the fact Andy was older and didn't need them in Toy Story 3, to coming to terms with the fact nobody wants them anymore because now they're old in Toy Story 4. Like, the only possible thing 5 could do is kill them all and bring things full circle with a new kid.