Because of the method of ingestion. Our lungs are a direct oxygen exchanger for our blood cells. When you eat or drink something its not immediately dumped into the blood stream. It gets processed through amino acids in tge stomach and then thru the rest of the filtering cycle. I.e., intestines, kidneys, liver.
When you inhale something, it goes straight into the blood stream via the silia in the lungs and bronchial tubes.