Why don't permaslows have diminishing returns?

This ties into mobility creep, but if you guys have played long enough you will recall that Ashe (her original design as permaslow archer) was the reason that a lot of fighters/tanks/bruisers were given dashes. Because dashes are the counter to slows, slows don't matter when you dash onto them.

But with the changes to rylais and the buffing to obnoxious levels of strength that frozen mallet received, permaslows are all to prevalent. You can't escape them. Even swiftness boots don't help all that much because they are constantly applied and swifties got nerfed repeatedly.

So why not give permaslows diminishing returns?

Sure, you can start at a 40% slow if you want, but after each second the slow should decrease and decay if it's from the same source. Ie, dot on rylais, auto attacks from frozen mallet, etc. Say 40%->30%->25%. So a decay rate of 25% effectiveness after each second (25% of the SLOW's value.) Diminishing returns from crowd control is important in games like MMOs because CC is so prevalent, especially from one character (it's not unheard of for a late game mage-like character to have 3-4 forms of hard CC in addition to damage) and while this cannot entirely translate to a game like league, the philosophy behind it is the same; consistent, constant applied forms of CC are extremely unfun to play against. That being the case, characters with more CC are typically immobile and have less damage. The problem lies with these two items:

Honestly these two items should just straight up be nerfed, but unless you change the slows on them they will have to be utterly dumpstered for every dps mage not to buy it. That's why I suggest diminishing returns on the slows, as once you are caught by anyone with either of these items, you pretty much aren't getting away. These two items are the reason that champions like Gnar, Viktor (up until recently), Cass, Brand, etc are so fucking dominant. Because it shores up their weaknesses (in the case of mages) or makes them insanely, insanely sticky (Gnar) while providing stupid amounts of health.

So either gut the stats (probably reducing health on FM is mandatory regardless) or actually fix the problem and make subsequent slows generated by these items less powerful. You shouldn't be able to land a Q as cass and make them move incredibly slow so you just hammer them with E's because they cannot escape. Permaslows are retarded. Gut this shit.