Is there a reason not to verify backups

All of us would, but those stand at opposite ends of the same continuum. It applies to cars we drive on the road, it applies to CPUs (I believe Meltdown to be an example of that) and pretty much everything you can imagine, including backups.

If we go back to the triangle "cheap, fast, good" where you can only pick 2 (borrowed here), speed is clearly something you chose OVER other options, at the price of degrading something else.

Finding your way out of this will get you many friends and many people who will be suspicious and take a closer look at what is done to "achieve" this.