Seizing boats also puts them on the defensive massively too, they desperately need that money, and the US seizing multiple claimed-superpower backed tankers is as clear a declaration of "we are serious about this blockade" as you can get without sinking them. Very few countries will put their neck on the line to save Venezuela of all places from this. So those troops are gonna be on high alert, night after night, while conditions manage to get even worse for their families - it won't take long at all until important shit disappears into the black market, and important people prioritize getting food to their loved ones over waiting beside a radar truck to get blown up.
They won't just fall apart and collapse casually or anything, but right now, time only benefits the US. Hell, this is probably legitimately good practice for the Navy and Naval Aviation, tracking narco's and letting their marines go cowboy on some oil boats.