CI 2.x->3.x file name changes cause url not work

It is a pretty bad habbit to leave the framework do the routing, and its mostly came from the CI community. No offens, it works, it fast, and hurraay, but if you get used to it and start working with other teams / companys on large project, your co-workers gonna kill you. Believe me:
 - You dont want to bound the routes to specific controller names. That could be really messy after a while.
 - The routes.php file is a great "app-map" for you and the entire team.
 - It is really rare. i dont 'member if i seen anything like this in other frameworks -> Whenever you have to work with for instance Laravel, Yii, Symfony, you will be happy you get used to write all of your routes, cuz in the most popular frameworks, you have to.
Good luck!

So ... it's bad, because everybody else does it differently. That's what all of your arguments boil down to. No offense either, but I'm fed up with "frameworks X, Y and Z do it differently" arguments.

It's different, that doesn't mean it's bad.
It has its limitations and downsides, as well as its advantages, just like other routing/configuration strategies.

It is far from perfect, indeed, but in the world of programming, everything is a trade-off - don't forget that.