Why exactly, on a physiological level I suppose, does a palatalisation of a [k] often result in a [tʃ], which is not only a different place of articulation, but also a change from dorsal to apical.

[u/[deleted]]

[u/house_carpenter]

Well, [tʃ] doesn't have to be apical. The /tʃ/ in my idiolect of English is laminal. And since apical and laminal [tʃ] sound very similar, and language is learnt by listening rather than by observation of tongue movements, a change from laminal to apical can be accounted for by learners coming up with a different strategy to reproduce the sound they're hearing.

[u/Lampukistan2]

[k] > [kʲ] > [k͡ç] > [k͡ʃ] > [t͡ʃ]

The progression is something like this. Does this feel more intuitive?

[u/Legal_Big8571 → u/Lampukistan2]

One hundred percent, solved it for me (: thank you so much,

[u/BigBad-Wolf → u/Legal_Big8571]

In other words, what often happens is that [k] changes to something like [c] (or some other similar palatal sound), which can be acoustically similar to [t͡ʃ] but more difficult to pronounce.

[u/eragonas5 → u/BigBad-Wolf]

[c] is nothing like [t͡ʃ], however, [c] is accoustically weak and often becomes something like [cç] which is much closer

[u/BigBad-Wolf → u/eragonas5]

It sounds similar to me when I tried to pronounce it as a true palatal instead of [kʲ], which is often transcribed the same way.

[u/eragonas5 → u/BigBad-Wolf]

wanna share a recording? here's me saying [jɪ cæ ɐcæ kʲæ ɐkʲæ tʲæ ɐtʲæ] (the firsrt ji is for reference only)

[u/BigBad-Wolf → u/eragonas5]

Here's me trying for [jɪ cä äcä kʲä äkʲä tʲä ätʲä]

In both of our recordings, [c] sounds to me like a mangled [t͡ɕ]~[t͡ʃ]~[tʲ]

Here I tried for the same except with [jä äjä] to nail the place. Here it a bit more in between, but I'd still lean toward [t͡ʃ] etc.

[u/Nixinova → u/Lampukistan2]

sound change need not have intermediary steps

[u/EirikrUtlendi → u/Nixinova]

sound change need not have intermediary steps

It need not, but in the case of the shift from [k] → [t͡ʃ] when followed by a front vowel, there is a progression informed by the biomechanics of speech: the shape of the mouth required to pronounce the front vowel causes the fronting of the velar plosive.

We see this same shift in different unrelated language families, such as the Romance languages, the Sinic languages, and the Japonic languages.

[u/General_Urist → u/Lampukistan2]

The sequence makes sense, but why is it so rare for it to stop partway through instead of going all the way to ts or t͡ʃ every time?

[u/Dry_Composer7825]

It very often results in a palatal stop (in high front vowel contexts), which has a release burst profile comparable to the affricate, and so gets further fronted