I guess “Plantae” seems pretty safe and intuitive for people who don’t know taxonomy, observers and unknown-sorters both. “Flowering plants” or even “vascular plants” might seem too technical. Plus if you’re an English speaker Plantae sounds like the word plant and that’s easy.
Not to mention the thousands of IDs made using this app which only does kingdom level IDs.
…or it’s entirely possible my URLs don’t do exactly what I think they do ;)