Because it is part of the lore
As they write here, BDs are like youtube is for people today:
The Braindance in original Cyberpunk lore very closely matches how the technology is depicted in Cyberpunk 2077, but in a very different context and manner. The braindance for average people in Cyberpunk lore is more often used as an enhanced virtual reality simulation, rather than an investigative tool as V uses it. Braindance functions more as another form of mass media, used to simulate the real-life events of another person vividly within the braindance user's body. Simulations in braindance record and display visuals as seen by the person's sight, emulates physical stimuli and muscle movements, as well as invokes emotions that the particular person felt in that moment, but within the braindance user's brain instead. It's essentially a full-body experience that simulates another person's memories neurologically.
In their official form, braindances are edited and managed by corporations and sold to the general public as forms of entertainment. Basically how in real-life how people can search up YouTube videos for instructions or watch Netflix for documentaries, people in Cyberpunk lore can typically use braindances to learn new things more efficiently or experience historical events pseudo-firsthand. Braindances can also be used as a form of emotional therapy. But braindances can also be recorded and acquired illegally using the black market, which can be very dangerous for viewers, especially if it's a "flatline" braindance (source person dies during braindance recording).
The issue as I see it, is that CP2077 doesn't really explore or make very good use of it, the first few times you do them, its pretty cool with all the stuff, switching between layers etc. But then it just becomes annoying, because first of all its scripted so its the same every single time, secondly there is no exploration in them everything is handed to you on a silverplate.
I think Angryjoe in this example demonstrate, pretty well how it feels once you have done BDs once:
Since BDs allow for anything basically, CDPR could have done so much more with this idea than they have. As it is now, I would personally prefer that it was just a cutscene or completely skippable, because they are not funny the second time, but are simply a waste of time.
Also I have my suspicion given the amount of effort put into the interface of BDs and hints from earlier trailers, that they had much bigger plans with them than what we are presented with in the game at the moment.