A month or two back, Zankza mentioned on Discord (while it was still up, RIP) how adding Apparel weapons can be difficult because they have to add glows to them as well, as opposed to Apparel sets.
There's numerous Apparel weapons which could be added which were top 1 era that were added at the same time - this includes Deadly Ruler as well I believe. (Beef Tendons, Deluxe Encyclopedia, Beef Tendons, Jeansui/Long/Triangular Ruler, Magic Pen, Beef Tendons, Sharp Dividers, Deadly Ruler, BEEF TENDONS).
I think Zankza managed to add glows to some of those weapons, but it was very poor quality so they scrapped it. Looks like it's the good old waiting game, as I doubt they'd release those weapons if they don't manage to fix the glows, because it's not their style to hastily release something of low quality.
I don't really believe they're not adding those weapons because it's a "waste of time", the demand for new apparel weapons is pretty high, I'm sure there's about a dozen posts asking for Deadly Ruler or any new weapon, some which even date back to long ago, so it's something that would probably be well-sold.