Great minds think alike?
One reason is very apparent. Various sci-fi series often employ the same people. For example, Ronald D. Moore wrote for STNG and is now the executive producer for BSG. In fact, Mr. Moore wrote the before mentioned STNG episode. Other reason may be lack of creativity or the inability to come up with something better. A lost energy signature is an interesting concept and there are plenty of vehicles available for writers to recycle this notion. Whatever it is, I am not at all upset or annoyed. Quite the contrary, I think it keeps us on our toes. You can always tell the die hard sci-fi fan who can quickly tell you what series, year, season and episode a reprocessed plot theme is from. Being a geek is cool!