It isn't really a specific font, just something AI models made to generate images have picked up on. Things that were immediately attention grabbing and bold probably got more positive scoring and reinforcement during training, so they learned to use larger more dramatic styles (this is also why you often see sort of electric or fiery glows, sparks, dramatic lighting, etc) but that doesn't really work to help a business stand out when all of them now look like that.

I'm also not sure if everyone knows this yet, but most AI image generators nowadays are split into two parts. It used to be that you'd need a prompt like poster, graphic, promotional, large text, dramatic, brushstroke font, on sign, city background, club background, microphone, This Font is the New Comic Sans bold text, high quality, but since most people do this shit through something like ChatGPT, and might just say "make me a poster that says 'This Font is the New Comic Sans'", in the background, an LLM takes that prompt and makes a more extended prompt for the image generator.

This is where a lot of this type of thing probably takes place. For example, I prompted an AI model with Convert this prompt: "Make me a poster for my nightclub" into a Stable Diffusion prompt for a poster, and it gave me: nightclub event poster, bold neon typography, vibrant magenta and electric blue lighting, silhouetted dancers in motion, smoke and laser beams, glowing geometric shapes, dark moody background, high contrast, synthwave aesthetic, centered composition, space reserved for event title and date, ultra detailed, sharp focus, professional graphic design, 8k (emphasis added by me)

Nightclub posters do sometimes have these elements, but a lot of them actually use clean typography, little to no neon inside the typography, it just made up synthwave as a relevant aesthetic to the club it knows nothing about, and simultaneously wants a dark and moody background... with something that has high contrast, neon lights, lasers, and lighting everywhere.

Both image generators and LLMs optimize for things that are bold and for excessive additions like you saw in the prompt earlier, which leads to the super sloppy, over the top, crowded designs you see on most AI posters.