Why are 'j' and 'ch' transcribed as /d̠ʒ/ and /t̠ʃ/?

[Glizdka]

Why are the sounds 'j' as in jump and 'ch' as in check transcribed in the IPA as /d̠ʒ/ and /t̠ʃ/?

These two look like the glyphs /d̠/ and /ʒ/, and /t̠/ and /ʃ/ stiched together. The problem I see here is that the glyphs /d̠/, /ʒ/, /t/, and /ʃ/ are already used to transcribe other sounds:

/d̠/ is 'd' as in day,
/ʒ/ is 's' as in casual,
/t/ is 't' as in topic,
and /ʃ/ is 'sh' as in shop.

This is very confusing. Are we supposed to produce two separate, distinct sounds, /t̠/ and /ʃ/, one followed by the other? Should we go 't'-'sh'-'e'-'k' when we say the word check? If these are meant to be single sounds, why haven't we invented spearate glyphs to transcribe the 'j' and 'ch' sounds? What's the benefit of transcribing these two sounds with glyphs already in use that are stiched together?

While it may seem quote-unquote "obvious" in English that these are supposed to be treated as one sound because there's not a word in English that uses /d̠/ followed by /ʒ/ as two separate sounds, there are other languages in which such words do exist. All of this seems like unnecessary potential confusion that could've been easily avoided.

 

[5jj]

The symbols /d/, /ʒ/, /t/ and /ʃ/ each represent a distinct sound which is a phoneme in many languages, though the phoneme /ʃ/ is often represented in writing in English by two letters together, sh.

In words such as hotshot, nightshirt, sweatshop, etc, the three letters tsh are pronounced as two sounds, /tʃ/.

In English, the sounds often represented by the letters ch are regarded as a single phoneme, an affricate, though phonetically they are made up of two sounds, /t/ and /ʃ/. The close link between the stop and fricative is shown in phonetic transcription by a tie-bar above the two sounds: /t͡ʃ/. (When I first studied phonetics many years ago, we ran the two symbols together in our notation: /(ʧ/.)

The sounds often represented by the letter j are regarded as a single phoneme, an affricate, though phonetically they are made up of two sounds, /d,/and /ʒ/ The close link between the stop and fricative is shown in phonetic transcription by a tie-bar above the two sounds: /d͡ʒ/. When I first studied phonetics many years ago, we ran the two symbols together in our notation: /(ʧ/.)

 

[Glizdka]

I don't get to see said tie-bars in most mainstream dictionaries, like Cambridge. When highlighting the text, it reveals it really is two symbols, not one. Is this just simplification/laziness?