Huh, you mean that like me and certain players on FG they simply main who they want instead of switching up characters? What a concept.
Not all of them, but yeah. They usually switch to higher tiered characters in order to obtain better results, since they are focused on winning. That is the main reason, but there are other reasons why they switch to higher tiered characters (like playstyle). Those who don't switch mains to higher ranked characters usually do it because one: the character fits their playstyle and it brings the most success, two: they believe in their character and they think they can bring the character to the next level, or three: they simply play the game for fun and isn't worried on losing. That last reason is most common in non-tournament settings were money is not on the line.
Of course, they are more reasons for both aspects, but those are the main reasons.
In your opinion, which characters are the most affected by this region bias?
Lucas, Duck Hunt (especially after Genesis 4), Lucario, Greninja (especially prior to Greninja Saga), and to a lesser extent: Dedede, Charizard, and Shulk.
I mentioned this in a previous post, but many players also focus on the character's main strengths, ignoring an overlooked factor of a character's overall strength: weaknesses that harms or nullify the reliability of a character's strengths, or it makes the character's own strengths flawed. I noticed that many of the characters people considers underrated (Shulk, Roy, Lucas, Falco for example) suffers from this. For example, Roy's combo game is flawed: as his sweetspotted moves are ineffective at performing lengthy combos past medium percents, while his forward, back and down throws are heavily reliant on reads because of their very low hitstun. Roy also has poor a approach despite his mobility owing to his slow air acceleration and unsafe aerials that cannot autocancel in a short hop. On a related note, Roy is ineffective at spacing: despite having disjointed range, the Sword of Seals' virtually useless sourspots force him to space his sweetspotted attacks dangerously close to opponents.
My personal tier list, which is at this citation, is modified from the official list to attempt to avoid those two things inflicting false viability (you might need to scroll down):
https://smashboards.com/threads/your-personal-tier-lists-anyone-can-input.452908/#post-21911905