What would we get if we would switch to another arbitrary looking value? Also other units are based on other constants not just the speed of light, so at some conversion you would have to use similar strange numbers, you wouldn't solve your problem you would just move it to elsewhere.
And you rarely convert to lightyears, so the strange numbers are outside, and everyday units fit nicely together with base 10.
And 1 liter or dm3 of water is roughly 1 kg, so the original meter is actually based on the density of water. It's very convenient that you can convert between weight and length in your head.
Water is based on meter? They drank only wine in the dark middle ages, Lavoisier invented water, I knew it!
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The point is your proposition doesn't make any sense, read the definitions of other units, not just meter, from the 2019 si standard. Lightsecond would become a nice round number, but e.g. 1 lightyear is 31557600 lightsecond so there you already have a strange number, but it's based on the rotation of Earth, a constant you cant redefine.