It's nostalgia. I prefer the older looks myself, but I don't hate the newer looks. Stuff has to be updated to keep younger audiences interested. Several will disagree I'm sure, but there isn't one kid in my family or extended family interested in OT Star Wars, or Star Trek pre 2007. It looks "old", outdated, and it moves to slow for them. But put on the Star Wars sequel trilogy/Disney shows, or Star Trek SNW and Prodigy, and they are enthralled.
The classic Monsters are the same, they just look silly to them. But MEGAN, Abigail, Smile, or whatever mascot Halloween Horror Nights uses each year...those are creepy/scary to them.
For me personally, it's definitely not nostalgia.
The Universal Monsters started in the 30s. As Dr. Phibes said, they had their magic, at least till the 60s. I wasn't even born yet.
And the Universal Monsters exposure in my region (SEA) especially in my country is not big at all. I never recall any of the classic movies aired on our local TV station. We didn't even celebrate Halloween here, there's no such thing as trick or treat, especially when I was a kid, in the '90s (nowadays there are Halloween parties of course).
But when I was first exposed to the classic Universal Monsters (late 90s), I was in love, right away. Even though it's weird at first because they are in black n white.. But of course, I saw Charlie Chaplin first, so I can accept it.
For me, the designs (especially those by the genius Pierce) are iconic. They are simple but effective, less is more.
I personally think 1931 Frankenstein's monster design is timeless. I mean, he basically wears stuff that people nowadays still wear: a black shirt, black blazer, black long pants, and boots. Even though the boots are exaggerated of course, the design is simple and actually modern.
I don't think he looks silly to our modern audiences.
Dracula wears a tux. Also modern, I think, even though there is a cape, but they can just use the modern tux design instead of giving him a Bryan Singer X-Men uniform.
The same goes for the other classic monsters.. mummy is always gonna be a bandaged zombie, the Wolf-man is well, the Wolf-man (they didn't even make any significant change on him aside from making him more beastly), and I think Milicent Patrick's design for the Creature is brilliant. They don't need to change anything.
Long story short, it was not nostalgia that hooked me to the classic Universal Monsters, it was their look. Their poetic design, and wonderful actors and artists behind the creation.
I don't like the newer look because I think they did not make an improvement over the classic design. They ditched the "class and character" and made it mediocre, IMHO. (No offense to the designers, of course, this is just my personal opinion
)