Dragon Ball fans often ask the question, "Why did Akira Toriyama choose Toyotaro?" because of how divisive the mangaka has been regarding the Super manga. However, it is important that many fans move past this question since it doesn't influence anything in the grand scheme of things and is missing the point for several reasons.
One of the most prominent is the fact that Toyotaro had to go through several projects before getting involved with Dragon Ball and also had the opportunity to work with Toriyama himself, allowing the latter to get a better understanding of his abilities. Furthermore, now with Toriyama's passing, the future of the franchise doesn't solely rest on Toyotaro's shoulders since there is a myriad of people involved in this.
Disclaimer: This article contains spoilers from the manga/anime and reflects the opinions of the writer.
Explaining why Toyotaro was chosen by Toriyama in the Dragon Ball manga and the context surrounding that decision

A major reason why Toyotaro ended up working in the Super manga was because he showed his ability to draw this franchise through his fan work, AF, and some small official projects, such as 2012's Heroes: Victory Mission. This was thanks to him submitting work to Shueisha to become an employee of theirs, which eventually got him to work with Akira Toriyama himself.
Moreover, it is also quite telling that Toriyama agreed to have him as the artist for the manga and worked with him for several years when he could have easily gotten a replacement if he wanted to. This is also emphasized by Toyotaro, who has stated in multiple interviews that the legendary mangaka constantly corrected him and helped him grow as an artist.
There is also the fact that both Shueisha, Toei, and Capsule Corporation, alongside Toriyama's family, are the ones holding even greater control in the franchise, with Toyotaro mostly serving as the one drawing the manga. Therefore, it is a bit more complex than simply stating that he is the one in charge of the entire franchise moving forward.
The comparison of styles

When it comes to a monumental franchise like Dragon Ball, inevitably, Toyotaro is always going to be compared to Toriyama, especially considering how popular and celebrated the latter's art and ability for visual storytelling are. That is an element that has been quite prominent in the Super era, with a lot of fans comparing how they draw and interpret different elements, such as action.
This is particularly telling in the manga-only arcs, such as the Granolah and Moro ones, where Toyotaro's writing and characterization have been given a lot more focus and creative freedom. However, despite some specific criticism, it is telling that a lot of fans want to see these arcs adapted into the anime, which goes to show that it has managed to reach a certain portion of the fandom.
Final thoughts
"Why did Akira Toriyama choose Toyotaro?" is a question that is always going to be quite prevalent in the Dragon Ball community, especially after the passing of the legendary mangaka. However, fans also need to move on from this point and understand there is a logic behind this decision.
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