I think you're quoting the wrong person there XD
I assume it's the old "if it ain't broke don't fix it" webtoons just by the fact that they are the biggest by a large margin means that creators will flock to them, bad interface or not, why waste money on the creators when the readers are what creators truly care for?
but that's just my guess it could be they are working on something or not I know just as much as the next guy =P
my sis is actually in a programming company, and this is true to some extent, a good team would actually release the product with as smallest bugs possible, doing years of QA and cleaning all the possible bugs before release and patch it out later if any bug gets through the filters. I'm guessing if webtoons wants to add a feature they would go about it, in the same way, =P it would take a long time but it is possible.