There's a good reason for that: in English, a trailing e tends to be silent, but also to indicate that the previous vowel is different (long vs. short usually).
So, to an English speaker, "lupe" looks like LOOP, which is different from "lup" which would be LUPP. Those aren't real words of course, so some similar words with this effect might be "flute", "lute", and "glute". "flut" and "lut" aren't words AFAIK (but "flutter" is), but "glut" definitely is, and has the short-u vowel sound as opposed to the long-u that "glute" has.
The pronunciation rules in English aren't very good and are full of exceptions, but speakers are still just trying to apply the rules they know, based on other words they know, to foreign names.