The "Floor" is used by Zos to refer to bad players without saying they're bad, just like low APM players is used to describe players who only use skills every few seconds which in general are bad players.

ZOS has been attempting to cater to those players more by nerfing many mechanics and introducing things like casttimes on ultimates, however none of this has to happen because the "Floor" is an self bred issue that gets fueled by how the game is designed.

Think back to when you started the game, maybe with the Beta, maybe in 2014 or maybe only 1 week ago. When you started the game you had not much of an idea about how combat will be and how this "interrupting" or "weaving" will later be integrated into the combat.
so you've spend your first few minutes with pressing random skills that you don't know much about and how good they are and pressed the buttons the game told you to, to get the introduction done.
that means you maybe interrupted and enemy once or twice, weaved 2 light attacks, and used your skills 3 times and blocked an attack from an enemy that deals no damage.

With this knowledge you're released into the starting zone, you mindlessly walk around trying to understand what is happening in the world and you start to do the first few quests which are pretty easy and every fight can be won without healing or performing any mechanics.
And here's the big issue this never changes in the overland zones, no enemy requires you to follow a mechanic, no boss will oneshot you if you don't block/dodge his attack and you don't see the effects of weaving skills and as you progress you start to forget about those things you've been taught during your first minutes in the game.

When you're reaching CP10 you're still not required to improve you can still level by doing quests, facing enemies who can't hurt you even if you just use light attacks without using any healing skills.

Suddenly you get into your first veteran dungeon with no gear, no idea which skills to use and what to do when an enemy has those red strings around him and you fail and you have no idea why the game became so hard.

This process is the equivalent of teaching your children basic maths for 9 years and then one day tell him to solve his first integral, doesn't sound like a good idea right?
However if you keep increasing the difficulty over the course of those 9 years the huge majority of people will be able to solve an easy integral without any issues and can improve on that further and will be able to solve differential equations at one point.

No one ever thought about making maths easier, you improve the teaching and implement a constant learning process which gives the majority of people the option to progress.

This is the attempt that should be used for this game too, you can have easy starter quests but it's important to constantly teach players and try to get them to improve, this removes any need to have drastic changes to match the floor and the ceiling because most people won't be stuck at the floor but will rather be in the middle ground where they can see that others are better but they understand why they're better and that it's possible for them to get there too by their own efforts because they have already improved themselves.