It is because the eye drops go through the tube which connects the tear duct and nasal cavity and then to your throat when you put put the eye drops in your eyes. Once the eye drops reach your throat, some of the eye drops may touch the back part of your tongue, and then you will taste the eye drops. So when you use eye drops, don't put too much of them a time. You'd better put 1-2 drops a time in your eyes.
Maybe it is possible to make you feel the eye drops flow your throat. Usually, the eye drops put in the eyes, and then will immediately get into the blood stream, and you can possibly taste them. But i never meet such problems when i use eye drops. You may need to practice how to use eye drops smoothly if you often use it.