Interesting point! I think the 2-5ml limit for open systems is more about safety and preventing leaks, especially with refillable tanks. Disposables might get away with larger capacities because they’re sealed.
Could it be about waste? Open systems are reusable, so smaller capacities encourage refilling and reduce waste. Disposables are, well, disposable, so they’re designed for convenience, not sustainability
From what I understand, it’s mainly due to how open systems are categorized under TPD (in the EU) and similar frameworks elsewhere. They’re often seen as more “modifiable,” so they’re given tighter controls—like the 2ml cap. Disposables somehow fly under the radar because they’re sealed and “single use,” which regulators treat differently… for now.