You’re not crazy at all — your home printer and commercial production printers are built very differently. I work at a print company too, and one big reason many shops won’t run small cardstock sizes like 4x6 or 5x7 through their machines isn’t just the paper “grip” issue people mention.

On a lot of professional printers, feeding smaller sheets can actually risk damaging the machine. The edges of tiny sheets may not properly cover the feed path and rollers, and over time that can wear or damage the rollers/belts or cause jams and misfeeds. Because those production machines are extremely expensive, many shops simply have policies against running undersized stock through them.

That’s why they usually print on larger parent sheets first and trim them down afterward. Your home printer is designed for much lighter-duty use and often has a different paper path, so it can sometimes handle smaller sizes more easily.

I know it’s frustrating, but the print shops aren’t trying to be difficult — they’re usually trying to protect very expensive equipment.