It most certainly is.

This is going to get a little rambly, so bear with me.

In law, religious/secular/government institutions, social interactions, entertainment, and all-around general expectations, marriage is considered the default adult romantic/sexual relationship style.

This, indirectly or directly, makes all those that choose some other form that aligns more closely with their preferences seem dishonest, suspicious, and untrustworthy to their married peers.  Add exponential degrees of difficulty if you also aren’t the following (especially in the United States).

• Straight
• White
• Vanilla
• Heterosexual
• Middle/Upper Class
• Religious (especially Christian)
• Cisgender
• Monogamous
• Parents
• Moderately Libidinous

No, annoying polyamorists/swingers and other non-monogamous people banging on about monogamy being “unnatural” is not a form of non-monogamous privilege.  It doesn’t even compare to the mountain of presumption and consideration married people enjoy.

Also consider the “sex-second delay” married people don’t even have to think about employing.  If you’re wondering what that is, just think what you would have to keep hidden, how you’d have to equivocate or generalize, and what you would describe in nonspecific terms if monogamous marriage (especially with the caveats above) was considered an outlier and you were repeatedly asked about your partnership status.

Complicate marriage (including plural marriage) with its oppressive past and present full of misogyny and abuse (think polygyny and the rule of thumb) and wonder no more why us resistant individuals don’t automatically see it as comforting, joyful, and pleasurable.

Think of all the unsolicited “helpful” advice single people get about finding partners and “getting hitched” when doing the reverse to married people would be considered unconscionably rude.  (“When are you finally going to get divorced/another partner/an additional fuck buddy?”)

So, yeah.  You married folks have it pretty damn good.  The rest of us would like an equal share of that good, if you don’t mind.