He’s free

@Starswirl  
Ew. XD

Or never married. Or the EQG world doesn’t use that custom.

It looks like he divorced spoiled rich (his wife) that’s my guess

@Ultra64  
Of course it is truth is often boring.

@Background Pony #9D05
 
But that’s the boring answer.

Don’t over think it hasbro’s animators mess up all the time.

@ChuymaruZ  
Rude.
 
It’s fun to speculate.
 
And for the record, I would.

do you use your ring all the time?
 
oh wait… I forget that Im talkimg with a forever alone guy… silly me

I suppose it’s the same sort of thing with Timmy Turner’s dad, or Dexter’s dad, or Cow’s and Chicken’s dad. Though, yeah, most of that is from not having an upper torso. X3

He hates rings. They cut off the blood flow to his fingers. :P

Nooo, but she’s such a lovely lady!

@Evil Emperor Proteus  
I wish Diamond Tiara would show up and scream at her dad because Dang it she’s going to camp in three years she won’t have that taken away from her!  
Unfortunately, it doesn’t look like she or the CMC will be in the movie at all. :P

How many married cartoon characters have wedding rings?

Shining Armor and Cadance aren’t seen wearing their horn rings after their wedding either.

Big deal. There are lots of married cartoon men not wearing rings.

I think it would actually be interesting to show that his character is actually quite different from his Equestrian counterpart simply to show that the characters can, and have, taken radical alternative paths in this other world.
 
Not sure if it’s a suitable topic for a children’s cartoon, but for all we know he could have divorced his wife in this world.
 
Anyway, I’m hoping that if Filthy Rich does get more screen time and a bit of development in this movie, that Diamond Tiara finally gets speaking roles in this one as well. It’s really overdue. This version of Diamond Tiara culd be a middle-ground of her caricature, she’s not mean to the Cutie Mark Crusaders because she has no reason to be in this world, and although not full-on antagonistic, she is a bit spoiled and sometimes bratty in that rich-girl kind of way.

Even in FiM: we haven’t seen Spoiled Rich and Filthy Rich interact. It’s not beyond the realm of probability that they’re divorced, which could also have contributed to DT’s attitude.
 
In fact, in Luna’s dream episode, Filthy Rich was seen running out of a house followed by a mare who was definitely not Spoiled Rich. Perhaps the two of them were having the same dream of each other before they were interrupted.
 
(Although, it was probably an animator oversight…)

Meta explanation is “animators likely forgot that detail”. But that’s boring.
 
He’s likely either not wearing it, as previously stated
 
@ImRaidAccount  

 
Or he’s divorced or something, maybe. While there’s admittedly no focus on DT & SS in the EqG world, they do come across as nicer (willingly participating during the cafeteria song, and the poster making scenes in RR, and not even background events of them being mean to anyone, not even the CMCs), which could be interpreted as either “Spoiled Rich isn’t a terrible person in this universe” or “Spoiled Rich is absent from DT’s life”.
 
I personally headcanoned “Human Filthy Rich is divorced”, but let’s see what happens.

Not to be that guy but he’s probably not wearing it.

To be fair, Mofo is sleazy without even bringing it up. His name is Filthy Rich… That’s like… One word away from Papa Franku. Related even… Papa Franku’s fam ain’ above mackin’ on high schoolers.