Animated TV shows are in a unique position in that the quality of the visuals is reliant on art style rather than expensive cameras, and with that, these shows evolve and change over time. Animated TV shows originally had to be hand drawn, before technology and digital drawing revolutionized the process to make creating animated shows much quicker and simpler. However, despite many shows now being created digitally, they can still undergo changes and advancements even as a show progresses from one season to the next.
https://screenrant.com/animated-tv-shows-jumps-quality-continued/