Not a ton of people in their 20s and younger can afford to buy a $400-$600 statue, at least not yet. Most of them might even have to ask for or get some funds from their allowance to purchase a $30 action figure of Deathstroke that's not George Perez-designed. Also, "classic" doesn't always mean the character's first and oldest look. It's the look that lasted for many years (decades, even), without or at least just minor revisions. Batman's blue/grey/yellow oval suit wasn't his first suit, but it was his look for almost half of his 78-year existence. At least 2 generations of readers and collectors grew up with that look.
Trying to modernize things on a $500 statue to appeal to a market that can hardly afford your pricetag is a faux pas. Like statues and high end toys, check out art collectors. Have you seen a lot of Adam Hughes art commissioned by a collector, which features a New 52 suit? NO. Because those who can EASILY afford a Hughes sketch are most likely those who grew up with the classic suits. The "newest" of all the suits Hughes would usually have drawn for a commission is the Darwyn Cooke Catwoman design, but that suit, is almost 2 decades old already and is COMIC ACCURATE. Art collectors below 20? They buy prints, $20 with free signature. Believe me, I know. You want to sell a Lightning Lad sketch for $300? Draw the one with the cape. Draw the hipster-hair version with sleeveless shirt, you'd be lucky to have it sold for $50.
So yeah, maybe it's an age thing to a degree, but not just in the sense of being old. It's about the present status of the collector. Older collectors are the ones MOST LIKELY to afford high-end collectibles like art and statues. While some might appreciate Sideshow's own take on the design, this would be the minority and Sideshow realized it, otherwise the ES for such a beloved character won't be this low.