Actually, it is an inconvenience.  Not only must they plan their trip, they have to plan their trip with the individual who is buying/selling the firearm.  And then hope everything goes well at the FLL.  A check can take 10 minutes, it can take 3-4 hours (I've had both), depending on staffing and how busy they are.  Or if there is a mix-up with records, it could last months.

And if you are denied because of a minor crime 30 years ago (like having a few ounces of marijuana), or an incomplete record that was never cleared up (like a co-worker of mine), you become a statistic for the gun control crowd as a 'domestic abuser or felon stopped from buying a gun".

Many people are now also finding a hard time selling their older firearms.  Why go thru all the hassle, time and expense to by used, when new is just slightly more?  Universal background checks are good news for gun manufacturer's.