car auto play in car stereo, why do I need an extra dongle?

[Willmont]

So I have bought Xtrons QB10X5CI with Car auto play support in my BMW F10 2014 with CIC system. When I try to use the car auto play feature, I have no idea to get started. After talking to the customer service, they said I have to buy another dongle such as the CP02 or CP03? I don't know why it still need an car auto play dongle to make it work?
why is this? Can't it integrate the dongle to the car stereo? Is is the same with any other car stereo?

[ADAMNUR94]

Some aftermarket car stereos support android auto, like XTRONS new product lines, they offer a retrofit kit to give owners the full Android Auto experience, i think it's the dongle you mention

[X5Sport]

For my last car (Škoda Superb 2016) the option was available but was a cost option, as is Apple's version for BMW’s. It can’t be retrofitted so there must be some hardware differences.