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.
I worked for an auction, and sellers accepted bids below the reserve price all the time. They just want to avoid a situation where an item sells at a “below market” price due to not having enough bidders in attendance - e.g. a single bidder is able to win the auction with a single lowball bid. If they see healthy bidding activity that’s often sufficient to convince them to part with the item below reserve.
Reserve prices are annoying for buyers, but below-reserve bids can provide really useful feedback for sellers.
We even had full-time staff whose job was to contact sellers after the auction ended and try to convince them to accept a below-reserve bid, or try to get the buyer and seller to meet somewhere in the middle. This worked frequently enough to make this the highest ROI group in our call center.
Also, consider this: if the reserve is too high, and no one bids on it, then everyone looking at it is going to wonder what it is really worth. If there are several other bidders, then that gives reassurance to the rest for the price they each are bidding.
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.