As noted by j01storm, people follow laws because they might be punished for transgressing. However, they also follow laws because it sets the rules of the game, which protects them from others. Take, for example, a game of football. Normally, everyone plays by certain rules of how you're allowed to tackle other players (no eye-gouging, no clipping, no excessive violence after the player is down) as much because they don't want to be thrown out of a game as anything else. But what if the "referee" doesn't really have any power, perhaps because you're playing a pickup game in the neighborhood? People still follow the rules, because, if they start tackling people dangerously, they run the risk of others following suit and attacking them. Thus, everyone keeps the peace and agrees to run by those rules, bending them at most, or breaking them covertly, but not doing so openly.
Admittedly, in the case of genetic sampling, this doesn't seem like something that would be a major issue, all in-house matters, but it might also be the principle of the matter, that they don't want to get into the habit of routinely breaking the rules lest the general structure of rules be seen as something that can be disregarded.