Why are there so many カ行、サ行、ラ行五段活用 verbs?


If you go into a dictionary like [Weblio](https://weblio.jp), and you look
through their list of verbs, you'll see that each of the consonant 行s of 五段
are in separate categories. However, there are a _ton_ of カ行、サ行、ラ行 verbs, to
the point that they have to be broken down into more categories based on the
usage or meaning of the verb. The other types - ガ行、タ行、ナ行、バ行、マ行、ワ行、ア行, only
have one category each. What is the reason behind so many カ行、サ行、ラ行五段活用 verbs
existing?

Additionally, does the ending of a verb have anything to do with the meaning?
I've heard of サ行四／五段活用 being interchanged in the past with Old Japanese [為]{す}
in サ行変格活用, and ナ行 is really only reserved for [死]{し}ぬ・[去]{い}ぬ・[往]{い}ぬ. Is
there any reason behind this?

