Never understood why can you bid below the reserve price, or more like why the reserve price is hidden because the whole point that they (the seller) have a price in mind they are not willing to go below.
It's the same reason an auction can go above the price/value of the thing, because you get invested in your $x bid, so $x+5 doesn't seem like paying $x+5, but instead "only $5 more to preserve your win" type of thing.
See penny auction scams - https://utahjustice.com/penny-auction-scams - for an extreme example.