Because most people don't know good racing games when they see them. Maybe I'm cranky because my Houston Rockets lost their series with the Jazz (again), but I'll show my reasons why. Forgive me if I seem to be too angry in typing this post up. Have a few minutes on you?
--- The Basics ---
Enthusia is so unknown simply because not a lot of people cared. It was just another boring GT4 clone to many people. GT4 and Forza were still battling among themselves. Most people don't really look on the shelves to see Enthusia. Read all the stuff I've posted showing my support of Enthusia Professional Racing. This is a good game. Maybe not a great game, but much better than what most people take it for. You could race on a track with falling precipitation- GT4 and Forza doesn't. You can race six cars on a wet track- Forza doesn't have any at all while GT4 had only 2 for a track. Enthusia has an amazing lighting system- GT4 and Forza lack this. It even has point-to-point events, a more refined rally racing experience than its competitors, and even downhill touge racing! But why did people not care? Not much exciting. You know, EVERY racing game has to be Forza- demolition derby damage, online play, six-figure exclusive superexotics, annoying and ear-bleeding rock music... and Enthusia was overlooked.
--- Reviews and Criticisms; True Fans vs. Mainstream ---
Just because a game has jazzy music and mediocre rock music (I did love Pacific Gateway's theme) doesn't mean it can't be a good racing game. If people weren't so stupid and insensitive as to what makes a good racing game (at least the bare essentials), people would have given Enthusia a better chance. But because of this, it's supposed to be collecting dust on store shelves and getting bad reviews by gaming media (according to the haters). All I ever read is "mediocre," "not very good," "cars driving like on ice," and stuff like that. Some of that may just be true. I just wished more people gave this game a chance. I love Gran Turismo 4. I've grown to respect the Forza series. However, more people should have given Enthusia much more credit than it deserved. But why didn't it?
--- Why Forgotten? ---
The politically correct answer is that this game didn't have too much to offer for the casual gamer. The personal (as in mine) answer is that most people still don't know what a good game has as opposed to how gaming is today. I'm still an old-fashioned thinker with games. I still always say that online gaming is never a requirement no matter who challenges my claim. A game doesn't need damage, but it helps. And if you do damage, do it right to the point where it's acceptable for casual gamers. Do it wrong, and it may prove too challenging and almost virtually unplayable. There was another game around this time that Enthusia was up against among racing games- "Burnout 3: Takedown." More people were either into GT4, Forza, or Burnout 3 than Enthusia. Racing games have nowadays been about crashing other cars. That's it. Racing's overrated, not everyone wants to be the next best racing hero, it's just about taking cars (licensed or non-licensed) and crashing them all day long. If a game didn't have this kind of ability to wreck cars, it was not worth the money. It's just all these things that contributed to Enthusia not being looked at with any real consideration. And this is one more thing in Enthusia's favor- it costed about 20 dollars... and well worth it even with $50 GT4 and Forza at the time. Konami must have felt like they failed their world of fans by coming out with Enthusia and not making it compete with GT4 and Forza (or just GT4 since this is a PS2-only title).
--- In Conclusion... ---
Why was Enthusia forgotten? The mainstream and all the greedy and obsessive things that mainstreamers make gaming dark horses look like lame ducks. For the rest of the world, Enthusia was a GREAT game no matter what IGNore, GameSpot, X-Play, or whoever the hell else have a bone to pick with this game. Haven't played EPR yet? It's cheaply-priced and a better game than what most people give (or lack thereof) it credit for. Find out yourself what mainstreamers and gaming media failed to realize about Enthusia.