Why do mint-looking LPs sometimes play poorly?

Groove damage, they've been played with a worn stylus
Poor pressing
Not cleaned properly, use disc doctor

That happens to me sometimes too. It's a bummer. I just paid a premium for a great looking version of Led Zep IV and then steam cleaned/Walker Audio Enzyme on my VPI machine and it's really noisey.

Bummer

Unlikely with Japanese, but dirt pressed into record at plant... brand new, still has surface noise.. also, brand new Japanese pressings can sometimes have a harshness esp. near inner groove areas, ? don't know why...
Second on groove damage, sometimes mint LP's have hacked up grooves but you can't see it... been there know all about it.
Conversely, sometimes dirty record bought used, once cleaned well, plays great like it was never opened!

Probably the original owner wasn't an audiophile and played it with wrong settings, too much VTF etc.
or
it was cleaned with RCM fluid which changed the structure of the vinyl. Vinyl from Japan is generally the very best when new.

records which are subject to poor storage conditions for decades can look spectacular. even some that are sealed.

I have had some success recleaning again than using microfiber towel and aquafina water pressing down firmly and spinning many times,then play and reclean with aquafina again.That cleaned up some noisy lp's I gave up on.I manually clean with the towel and water.Sometimes it works.

I have always cleaned my vinyl before it is played. I am now recleaning all my vinyl because the vinyl is much quieter with a final rinse with Aquafina water.

Some vinyl formulations are inherently noisy

Jaybo, can you please clarify what you mean by "poor storage conditions"?

Macdadtexas when steaming i ve noticed if you get a record that has a lot of dust and debris on it before you use a brush on the LP first pass the steamer lightly and then vac this will get most of the debris off the surface before you start brushing doing this results in a better playing record.

Using a double rinse is key to a great playing vinyl record. Sorry to get off the subject.
Mike

>> Why do mint-looking LPs sometimes play poorly?<<

Because, according to The Temptations, "Beauty Is Only Skin Deep".