EI was developed mainly in response to folks that had no test kits that lived in 3rd world countries and for lazy/cheap folks.

Some folks like dosing daily, when they feed their fish.
Some forget to dose 2-3x a week(uhhh was it on Tues or Wed I last dosed the traces?? ahhh......????.), so a daily routine works better for their habits.

Some have a tiny tank and want more consist ppms in their dosing than 1/64 th of a teaspoon can afford. Whatever your reasons, this is just an example. If you have high PO4 in the tap, add less KH2PO4, good GH, skip the GH booster etc.
If you have high NO3 in the tap water, skip the KNO3, use K2SO4 in place of it.
This is an example of EI for a 28 week supply for a 20 gallon tank for those with teaspoon aversion.

To 1 liter of DI water add:

60 grams KNO3
10 grams of KH2PO4
25 grams of GH booster

Add 5 mls of this solution daily.
Add TMG at 2.5 mls daily.

That's it.

That's EI without the teaspoons and more accuracy in dosing.
If you fiddle with daily dosing, you may have a better routine
and habit. Some are okay with 2-3x a week.

You can scale this up or down to suit your tank volume, light level etc, make larger batches etc.

But if you are not and skip dosings etc, then EI may not give the same results using 2-3x a week dosing as daily.

Thus it is not the method that fails, it's our own habits and routines.
Still, this gives a PMDD type routine for folks to do.
PMDD uses a similar routine and nutrients, but leaves out PO4.
That was due to the hypothesis that was falsified later that PO4 limitation controls algae and limits them.

Teaspoons are just easier to explain and most folks do not own a scale etc.
Plants are not these sensitive things, nor should your tank be either.
They have a wide range they can adapt and grow well in, thus such accuracy is not critical as some will have you believe.
Anyone with common sense can see and test that themselves.
EI nor any method was ever meant to be rigid. You finess and tweak to suit.
Often we think what we did is really causing an effect. Often it's just we are paying more attention to the tank.
That can help any tank as we all know.

Regards,
Tom Barr