As an additional lens on examining less popular and/or newer words: All of these [kipisi, lanpan, meso, misikeke, soko] can be restated with the more popular words as Deni pointed out, but there’s also an is-this-essential argument that comes up with respect to words like leko. leko is popular, and widely useful, but still possible (though inconvenient) to express among the collection of popular words without using leko. It also wasn’t in the original definition of the language. The main argument against using leko, which also applies to the words you list here, is whether or not the concept is necessary to refer to in regular conversation. We’re surrounded by leko things all the time- stairs, buildings, boxes, blocks in Minecraft, etc. But how often is the fact that these things are square the most important thing about those objects? Comparatively, much less often. Stairs are path to go from one place to another- a nasin. Buildings are a place to stay and be safe from the elements- a tomo. Boxes are a place to store things- a poki. Even blocks in Minecraft are something else in addition to being blocks.
In short, Toki Pona as a philosophy/language hybrid wants to strike a balance between minimal and practical. There’s no need to include a word just because it covers a semantic gap - it may not be all that important on a regular basis. Simultaneously, there is no need to remove a word just because it overlaps with another. Sometimes the extra specificity is valuable, even in a minimal list of words.
The trick here is that different speakers will disagree on where to draw the line, and their opinions on where to draw the line will change as they learn more as well! And this is something I personally find incredibly enjoyable about Toki Pona.