"The Fair has seen an uptick in incidents involving high school students in recent years, a spokesperson said. With new city contracts requiring the Fair to cover all the Dallas Police Department's expenses and security costs—more than $8 million for the 24-day event—unpredictable attendance spikes from high school groups have become a bigger concern."

TBH it sounds like the change that requires them to cover all the DPD costs is probably the biggest issue--it leaves the fair in a situation where they need to cut costs where they can.
From some research (I mostly looked at the council on criminal justice's page for info FWIW) it looks like, overall, juvenile crime is lower that it was in years past and it hit a low in 2020--but it has been ticking upwards since then and there has been some indications that social media has lead some younger people to participate in 'flash mob' style criminal behavior (we've all probably seen people block off the highway for drifting/racing/etc. and there are incidents of flash mob fights and things like that) so the fair is certainly an easy target for stuff like that and would explain the fair's report that there's been an uptick in incidents.

Plus, they mention the unpredictable spikes which makes sense--if the fair is used to keeping low staffing (including security) during the day and then a large group of high schoolers all come then that can throw things for a loop.

I imagine the printing costs and the low usage aren't really the biggest concerns--it's the need to cut costs where possible and they don't want to maintain a higher than necessary staff/security level at all times on the off chance a huge group of teens will randomly flood the fair. This probably allows them to more accurately predict when attendance will be high/low so they can staff accordingly.

It sucks, but I get it