You're not thick at all. The compensation issue is tricky to understand, and most people just avoid thinking about it.
Compensation of the 3rd string by lengthening it at the bridge does indeed mean the 3rd string frets accurately as you fret it going up the neck. Lack of compensation is even audible as the string frets sharp even at the 4th fret -- which is why most players avoid playing the "unison" of the 4th fret of the 3rd string with the 2nd string open. Most banjo players have ways of avoiding using the 3rd string up the neck when its being a little out of tune will stick out. They will find the same note on the 2nd string (a few frets higher) if the exact pitch is important.
Since compensation tends to cure this problem, why don't all players use compensated bridges? For those, like myself, who are looking for a certain banjo tone, it's because of tone quality. Many of the compensated designs seem to disrupt something about the "popping" sound quality of the banjo notes, that straight bridges tend to not disrupt.
The fact that "our leader" Earl Scruggs and many of his closest imitators don't use compensated bridges is probably still pretty influential in why they are not "standard". My hunch is that if a bridge design came out that combined optimum sound with good compensation, then a lot of players, myself included, would use it. Compensation of banjo bridges is still a pretty new thing, having been introduced maybe 30 years ago. For a while, there was only one design, which not many people liked the sound of, but in recent years, there have been more and more designs, and that shows promise for the future.
In the meantime, most players just avoid the most obvious problems with the sharp fretting of the 3rd string, using the method described above.