Why aren't there kpt-changes in the verb maksaa?

Katja asks: 
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Why kpt vaihtelu does not take place in the word maksaa? Why k doesn’t disappear but in nukkua it does?

My answer:

KPT vaihtelu, KPT-changes or consonant gradation are systematic changes that happen in the different stems of Finnish words. If you’re new to these or just want to brush up on what you know, start by reading this lovely post on the brilliant website Uusi kielemme.

For a lot of people, the best answer to your question is “because that’s just the way it is”. Many of my students find that it's the best to just learn the different stems of any word you learn by heart. Luckily, that will also happen naturally and on its own after a while, because you will see and hear them all the time when you’re reading and listening to Finnish. It will just start sounding better to you to say minä maksan and minä nukun.

The rules are really nice to know about though, as it helps you remember the patterns and makes it all feel less random.

But some people learn best by learning the rules and appliying them. The important thing is to know what works best for you! So, here goes for those who love grammar rules:

KPT-changes only happen at the last syllable of the stem, so

nukkua - to sleep
strong stem: nukku-
2 syllables: nuk-ku

The last syllable -ku has a k in it, so a kpt-change happens (kk: k), and the weak stem is

nuku-
minä nukun, he nukkuvat

lukea - to read
strong stem: luke-
2 syllables: lu-ke
the last syllable ke again has a k in it, so a kpt-change happens (k goes away), and the weak stem is

lue-
minä luen, he lukevat

maksaa
stem: maksa-
2 syllables: mak-sa

There's no k, p or t in the last syllable, so no kpt changes can happen and the stem stays the same all along

minä maksan
he maksavat

However, there are some exceptions, as always (kiitos suomen kieli!):

1. When you start with a stem that is weak, it's not always possible to see that there's a k in the strong form, you just have to know, like with other verbtypes than verbtype 1:

pelätä
strong stem: pelkää
minä pelkään
he pelkäävät

2. Also, sk, st, tk and two vowels don't participate in kpt-changes, so
ostaa
stem: osta-
minä ostan
he ostavat

And a handful of other stuff to mix it up, which I won’t go into here! If you want to know more, go to Uusi kielemme and read this post about consonant gradation puzzles. 

What is your experience in learning and appliying kpt-changes? Are you a person who learns best through learning the rules by appliying them, or do you learn best by learning each word individually? Or maybe something in between? 

Breather in, breathe out and read about kpt-changes in Finnish verbs!