The only ones that aren't horrible manage that because they're so bland there's nothing to go wrong. Look at an example with some detail, the "Now please make one in the style of a 90s drum n bass gig flyer, with early 3D/fractal computer imagery" poster.

At the top of the page we have a deformed wireframe sphere. A wireframe sphere is stylistically appropriate, but the incorrect rendering is not. The "CGI" aesthetic requires obviously computer generated lines, which in the 90s meant accurate and regular lines.

Next we have a messed-up stellated polyhedron, and a messed-up dot pattern. These also fail for the same reason. The main 3D rendering is also obviously broken, as are many other small details.

But the biggest failure is the complete misunderstanding of the culture. 90s DnB was absolutely not about "good vibes". The smiley face logo is completely inappropriate; that's associated with late 80s/early 90s rave culture, pre-DnB era. 90s DnB was much darker and edgier in tone. The scene was almost exclusively male, and it maintained a aggressive vibe carried over from jungle.

A 90s DnB event would never advertise "bringing communities together". Audiences would be repelled by such messaging. This is despite it actually doing just that, as the scene was racially integrated in a way that mainstream music at the time was not. If there's going to be pro-social messaging on the poster it has to be there only implicitly.