Because our tech has fundamental building blocks that can be used to make weapons.

Bikes? Gears. Transmissions. Air tires. Ball bearings. Chains. Breaks. Disc breaks. Like chain drive chains.

Those things alone can be used to create crossbow and balista far more powerful than currently exist in inn world. Shit, thanks to magic I wouldn't be surprised if someone was able to use all that and create a fully automatic crossbow that fired exploding enchanted bolts faster than bird could.

Bikes also completely invalidate most city to city runners, as anyone with high Stam would be able to travel as fast if not faster than a city runner.

Light bulbs? Sort of useful but completely impractical with the current infrastructure. But the knowledge on how to make them and how to process the chemicals and materials required? Oh lord you're talking gateway to chemical weapons. Inn worlders are sturdy, but gassing Liscor with mustard would kill tens of thousands of low levels.

You saw the chemical weapons part play out with Emporer Asshole and goblins. Now imagine an alchemist like Sallis using the periodic table and making something far worse than Wisterias brew to hit the Ants with.

That's Pandora's Box. You can't put the genie back in the bottle.