Yeah, as far as I know, Space Marine power armour links with its wearer via matrix styled plug-ins.
That allows the Space Marine to project a HUD directly into his eyes / brains for example.
Depicting his Squad's status and aim assist.
.

Also Power Armour absorbs excretions ( sweat, urin, etcetc ), recycles it and feeds it back to the Marine.
I think its just a case of Chaos Wargear beeing much older and more archaic.
More Modern Power Armour types also tends to cover up potential weakpoints, like the Mk8 that covers the cabels / pipes that lie exposed on earlier armour variants.
Alternatively it just could be a case of these Chaos Marines melting / fusing together with their armour, after spending so many millenias with it, exposed to warpenergies.
( I think loyalists remove it daily to clean it if not on mission, dont see Chaos Marines doing the same )
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Especially Terminator Armour I believe
needs these kind of implants plug ins to operate to its full potential.
If I remember correctly, in the TT, Inquisitors in Terminator Armour didnt get all the adventages out of it ( the additonal melee attack if I remember correctly ) because they didnt have the necesarry plugs to their nervous system.