It is my view that companies have the obligation to make information available about their products and do so in an easy-to-read manner, everything else is consumer's choice. Your comparison lacks relevance in my opinion.
(and in cases where someone asks stupid questions, which can be easily answered by looking in the manual page, yes... please read it...)
If you're trying to make a normal diet healthier, then the amount of unnecessarily added sugar becomes much more relevant. It tells you when you need to find a better brand, improving the health of your food without disrupting your diet.
And to do that, you need to read and decode the ingredient list. Doing this for every single food you buy is slow.
When it comes to RTFM: Sure, read before asking, but if something was confusing in the first place it's often the fault of the design. Don't let yourself forget that.
Which would reduce sugar, and quite likely be unhealthy for all kinds of other reasons. Overreliance on sugar may be the most common problem in modern US diet, but that doesn't mean that a naïve and monomaniacal effort to reduce sugar won't result in some worse problem.