As the comment you're replying to points out, that same opportunity cost applies to literally any non-essential ~$20 purchase they made with any currency in that time period.
If I approached you in 2012 with two envelopes, one with $20 worth of US bank notes, one with $20 worth of Bitcoin, you'd most likely take the cash. If I approach you again in 2021 with the same envelopes (unopened) from 2012, only a fool would take the cash.
Speculative assets would not exist if your theory held water.
If Monty Hall asked you if you wanted to change doors before opening one the problem would not be much of a problem.