Simple answer? Because, just like with their proposed TM control changes, it makes fights too "easy".

As an example, I highly doubt they intended Spider 20 to be clearable in 10 seconds. It literally lets you skip every one of the mechanics that make the fight a challenge. And if they don't change the way the skill interacts with the bosses, they cannot make those fights more difficult/rewarding, because all it will mean is you'd need slightly better gear.

The same applies for the TM control changes. They can't make FK21-25 more rewarding without nerfing TM on those fights because, if they leave TM as-is, the only thing those higher levels will mean is slower fights.

I actually think making these changes for 21+ only is both fair and relatively easy way to add some additional strategy to existing dungeons.  Nothing in the game today is impacted so it really isn't a nerf. So no more crying from you guys with 3 septimus, 5 royal guard and 6 coldheart. Lol. 

It definitely was a nerf when they applied those passives to the DT bosses, but in this case, indeed, it's fair enough. At least, as long as levels 21-25 merely give you better chances at 6* legendary gear, not some new super-powerful gear that becomes the new requirement for progress. 

If they made it more rewarding, it would maybe not be so bad. But there is no hint of that happening and I doubt it will ever happen.

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It's still a garbage slap in the face. But it is kind of hilarious in its stupidity.

Community: "It takes too much time to play the game."

Plarium: "We have a fix! New dungeons are going to take even more time!" 

I don't understand why you expect it wouldn't be more rewarding. Why do you assume that the reward progression would not continue at the pace it did from 1-20?

My expectation is that, from 21-24, your chances of getting a 6* will continually increase, and, at level 25, you will only get 6* drop, rather than 5-6*. 

I truly don't understand your complaint. Generally, people are happy when games provide more difficult challenges to overcome - I mean, that is the whole reason of playing a game, isn't it?

It can become a hard nerf if the requirements for future fusions are rising according to the new parameters of Dungeon levels 25 being present in the game.

Yes it's a stupid change.

Max HP damage is fine. Doing clears fast is fine. 

The challenge comes from maximizing your speed, not from the dungeon itself. 

How is that bad?

It's a mobile phone game, already it takes several hours to finish dailies, now dungeons are gonna take 10 times the time they did, why? Is it a challenge if it lasts 3 min vs 10 sec? Absolutely not. 

The only thing that's gonna feel this 3 min dungeons challenge is our phone batteries. Stupid design. 

Especially since I've heard you can STILL get 5* rare gear drops.

You can't let people build in a specific way for 2+ years and then switch the meta upside down and think it is a good thing for the game. 

Well... if they haven't thought about these possibilities, it just shows that they do not play their own game or are very bad at game design.

If they design a skill like *damage from MAXHP* and introduce it into the game, they should not be surprised that players are using this skill. 

If they design DoomTower for months and declare it Endgame, they should not be surprised that players being in the former endgame for years have the champs and equipment to solve the new endgame in very efficient ways. 

If they design Doomtower for months, they should have taken the usage of turnmetercontrol and MAXHP into consideration.

But they released the Doomtower and were surprised that it is beatable in short time with the mechanics in the game, which they implemented themselves!

Afterwards changing the mechanics of Normal and Hard instead of bringing in a brutal Doomtower with these changes just show, that they are not good in designing game modes. 

They are brilliant with graphics and animations....but honestly...missing Dupe system, Silver costs, Arena problems, missing filter options for champs...etc...show that their goal is not to provide a fun game but a money maker. 

Astonishingly, I agree with you

I don't think that's really fair. They are ordinary people who make mistakes just like anyone else.

I truly believe they did not expect all of the tricks people have come up with, and to their credit, rather than fixing existing content to make those tricks not work, they are adding new content.

But ultimately those tricks are part of the reason why we play Raid and why it's such a successful game.

They shouldn't remove a feature they (un)willingly added and slap the playerbase in the face.

Rather, they should build the game around it since it benefits the players especially those with shorter free time.

Who does longer dungeons benefit exactly? Not Plarium. Not players. Noone.