Shovel Knight will be getting a price increase to $40 by April 2019

People who buy the game at launch end up feeling as if they got scammed

You are obviously not one of those people so don't speak for a group you are not a part of. If I'm buying a game the second preorder becomes available then that's because I'm comfortable with paying the amount of money it costs at the time. You agreed to that price back then and pretending that you're victimized because today someone may get a better deal than you did yesterday is disgustingly entitled behaviour.

Imagine buying AC Odyssey at launch for $60, and then finding out a month later that its $30

Change that to 2, max 3 months and that's exactly how the used console market looks like. And surprise surprise, both day one and used copies have their audience and absolutely no one complains because everyone knows how this situation looks like and can choose the option which suits them best.

I think developers should stick to one price and make customers feel as if they made a good decision

A good decision regarding what? My pathetic, worthless self humbly donating $$$ to the Glorious Perfect Developers during a timeframe they wanted me to?? And the alternative being either a price increase "punishment" or being told the scummy "if you don't like it then just don't buy it lol" strawman?? This is absolutely insane

I understand buyer's remorse is a thing, and it sucks when something goes on sale right after you bought it. Thankfully that's not such an issue with Steam since they began allowing refunds. That said, most people buy entertainment products with the understanding that the price will go down over time, so the game you're paying $60 for on launch day will probably end up selling for a quarter of that in a year or two. Yet with Steam games, you have people basically saying, "I paid $60 for that game a year ago! Why should HE only have to pay half that?" I'm not talking about a game getting a sharp discount a month after it's released. That's the exception rather than the rule.

And yes, developers and publishers profit from consumers' impatience. They count on it. People who pay full price on day one because they've GOTTA HAVE IT NOW are just like the people in F2P games who pay to unlock things that they could get for free by grinding because they've GOTTA HAVE IT NOW. And that creates two tiers of consumers. You've got the ones who have to have what's popular /now/, and want to be a a part of the scene surrounding it - discussing it on messageboards, being a part of the online scene for that game if there is one, etc. - and the ones who are willing to wait a year or more for a good sale, when the game's "old news", the online component's dwindling or dead, the discussions have died down and all the twists have already thoroughly discussed. And I don't see anything wrong with that. That's not a "slap in the face" to the day one purchasers, even if they think it is.

tl;dr: If people don't want to wait for a discount, they shouldn't demand that everyone else be forced to pay the same price they did, or complain that sales are "unfair" to them.

I think perhaps the thinking is that by releasing the new campaigns as straightforward DLCs for the original game they might get dismissed/ignored and/or 'lost' in the sea of offerings more easily than if you take that same content and then release it both as a separate standalone experience as well as a notable update to an already existing game. For existing owners Steam in general does a pretty poor job of help making you aware of when there is new DLC becoming available for your games. And for everyone else who is a potential customer it doesn't seem like DLC is promoted on storefronts quite the same way that full games are (even when it's a 'big' DLC arguably worthy of the old traditional expansion pack status) nor like they tend to make the trending feeds or other avenues of visibility that they do -- and even when they are newsworthy it seems like it's more the exception and not the rule for DLC to make significant headlines for a positive reason. Because everyone and their mother seems to be trying to make and market games these days and with Steam opening the floodgates starting with Greenlight, discoverability is a huge problem for developers these days just with base games, let alone adding in DLC to the mix. So does this work? I don't know.

"We’re hard at work putting the final touches on King of Cards and Shovel Knight Showdown. After more than 5 years of development, the final pieces of the Shovel Knight saga will be complete! To celebrate this momentous occasion, we want to give everyone one last chance to get Shovel Knight: Treasure Trove at the lowest price ever! Remember, after the final games are included, the price increases to $39.99 (USD)!"

Think that will be it. Yeah they do seem to be milking it especially if you still sell Specter (normal price $10) when it's seemingly already included in Trove.