The MCU has a history of playing with the greater Marvel lore, but arguably no aspect of the comics has changed more than the cosmic characters. James Gunn has made some pretty substantial alterations to the Guardians of the Galaxy world, and while fans have responded positively to most of the changes, it seems that one aspect of Yondu didn't sit well with them in the first movie. In the face of that fan response, Gunn's remarks on the commentary track for Guardians of the Galaxy Vol. 2's upcoming home release indicate Yondu received his bigger fin as a response to the backlash. The director explained:
Yondu became a space pirate, and not a sort of Native American-inspired spiritual warrior that he is in the comics, but people very rarely get upset about any of that. It seemed like the one thing that people got upset about was Yondu's small fin. They somehow thought it was important that Yondu had a big fin. I don't understand what comics fans get upset about over something else they don't get upset about. That something so physical and small would be the thing they'd get upset about, but they did -- and in a nod to the fans, who I'm appreciative towards, we gave them the big fin.
James Gunn changed a lot about Yondu as he adapted him from page to screen. In fact, the character is almost unrecognizable in a few key ways now that Michael Rooker has become inextricable from the part. However, it wasn't the core personality changes that seemed to bother fans; it was the short and stubby fin worn by the character to guide his Yaka Arrow. As you've already gleaned, certain fans didn't love it. However, Gunn has become known as a filmmaker who embraces fan-service, and as such, he ultimately found a way to make the fans happy by giving Yondu the fin they all know and love -- before sending him off with a selfless sacrifice.
Yondu is still a far cry from the version of the character seen in the comics, but the larger fin at least seems more in-line with fans have come to expect.
It doesn't seem likely that James Gunn has any intention of moving away from these substantial changes anytime soon. Although he eventually acquiesced and gave Yondu the bigger fin, he has mostly adhered to his alterations to the greater Guardians lore and made this corner of the MCU his own. The finale of Guardians of the Galaxy Vol. 2 suggests some serious expansion of the cosmic universe -- particularly with Sylvester Stallone's Stakar and the rest of the Ravagers -- so we may have only scratched the surface with regards to how James Gunn will continue to evolve the Marvel mythos to suit his style.
James Gunn's Guardians of the Galaxy Vol. 2 is now available on Digital HD, and the Blu-ray and DVD editions of the film will hit shelves on August 22. As for the rest of this year's major releases (superhero-related or otherwise), take a look at CinemaBlend's movie premiere guide to see what else 2017 has in store!