This is an excellent point!
[Note: I'm not saying that bitcoin is "legit" - I have only read a few things on the topic and, although I understand some of the cryptography behind it, I don't know if it's "legit" or what that even means in this context.]
Right... because things that are "legit" are easily understandable in 2-3 small paragraphs. Such is the case with quantum mechanics, computational fluid dynamics, vector spaces, lambda calculus, external polyphase mergesort, and so on. But onwards...
If you
really wanted the 30 second executive summary, how about the following (slightly edited) intro from wikipedia, which is only one paragraph:
Bitcoin is a peer-to-peer payment network and digital currency with a public transaction log introduced in 2009. It is sometimes called a cryptocurrency because it uses public-key cryptography. When paying with bitcoin, no actual exchange takes place between buyer and seller. Instead, the buyer requests an update to a public transaction log, the blockchain. This master list of all transactions shows who owns what bitcoins currently and in the past and is maintained by a decentralized network that verifies and timestamps payments using a proof-of-work system. The operators of this network, known as "miners", are rewarded with transaction fees and newly minted bitcoins.
This accurately describes what happens, at a high enough level of abstraction for just about anyone.