Wild garlic (Allium ursinum, German: Bärlauch) is a native plant and not invasive in Germany. It’s not like it’s everywhere as it usually needs alluvial, deciduous forests but common enough that most locals usually know a spot or two. It may look like lily of the valley (Convallaria majalis, German: Maiglöckchen) or autumn crocus (Colchicum autumnale, German: Herbstzeitlose) which are both poisonous but that’s not the reason why you’re not allowed to pick large amounts. The Federal Nature Protection Law (Bundesnaturschutzgesetz, see paragraph 39 for details) forbids the collection of any wild plants or animals, independent of their protection status to disturb natural processes as little as possible. However certain exemptions are possible, think hunting, fishing, or the collection of wild herbs for example. While the former two require a license and are restricted to certain area or seasons, the latter is limited by the amount you may take. It explicitly states to only take amounts that are for personal use and that commercial collection is prohibited. It’s obviously to prevent overexploitation. Unfortunately, it’s not uncommon that naturally occurring stocks of wild herbs, mushrooms or berries are used up and destroyed by illegal and unsustainable usage. Also, yes wild herbs are commercially grown on farms but as you can imagine, they don’t come cheap at all.
Because there’s a whole range of processes involved in whether or not a pathogen can infect an organism (mode of transmission, various barriers including immune response, etc.) and a whole different range that determines whether or not an infected organism can spread a pathogen (mode of transmission again, viral load, vector capacity and competence, etc). For instance: assume the pathogen can infect an organism but can’t replicate often enough to reach the required viral load in the host to spread further via it’s usual mode of transmission. We’d end up with a dead end host instead of a pathogen reservoir/vector and the chain of infection would stop right there. That can be seen in the West Nile Virus for example when it infects humans or horses instead of it’s normal host: birds. I don’t know enough about influenza to tell whether that’s a thing here or not but I hope it clarifies why infections are often not that straight forward especially if they involve zoonotic events.