It’s a whole thing like “football”/“soccer”. I’ll give the short and imprecise.
Richard gets shortened to “Rick” or “Rich” most commonly. Certain fads in language tend to occur. Like using Z instead of S or using X like “xtreme” and so on. Long ago- rhyming was quite popular. So “Richard” would be made to “Rich” and then Rich rhymes to “Hitch.” So- Richard when shortened to “Ric” which then is changed to line up with English as “Rick” is rhymed as “Dick.” Far less common Richard can also be “Hick.” This is thought to have to do in part to the difficulty/expense of writing/printing lending people to look for shorter ways to write things.
We see the same rhyming nickname transformation where Robert becomes Rob and Rob gets Rhymed to Bob. William>Will>Bill. With Women- Margaret becomes Marge or it can become Maggie. Maggie would Rhyme to Peggie loosely. Maggie and Peggie often become Mag or Mags and Peg respectively. So Margaret might become Peggie and then Peg. And of course there are variants and cultural versions of similar names as well and so on.
The diminutive is somewhat random and culture based. But usually a nickname tends to carry either a simple shortening for the sake of brevity (Richard>Ric[k]) or some manner of whatever sounds pleasant to the ear of the culture. For example- Ever notice that “English” names very rarely end on a vowel- in Japan, names like Yoko, Yuki, Yumi, Chiharu, Kuro, Hayato etc etc. are common. Last names like Kobayakawa, Honda, Tanaka.... etc etc. Greek and Italian also have vowels as more common at the ends of names for example.
So you’ll see “cock” (don’t laugh) as a popular suffix for a time. Babcock and Hitchcock and Cockaran, Wilcox and even just Cock and so on. Cox is believed to be derived from Cocc- meaning the little” or “Cock” as in a heap or mound. Cocc would be ascribed as a diminutive in a manner of endearment like “Little William” which could become the last name “Wilcox.” Likewise Cock as in mound could be given to a person from the hills of near a hilly region.
And thus it is by whatever the zeitgeist of language is in a time or region which makes some sound more favorable that we get these participles and conventions. That’s how “Dick” stuck around for Richard and “Hick” did not- with “Hitch” holding on but being far less common- just what sounds “right” or best to people in a given time or place.
Richard gets shortened to “Rick” or “Rich” most commonly. Certain fads in language tend to occur. Like using Z instead of S or using X like “xtreme” and so on. Long ago- rhyming was quite popular. So “Richard” would be made to “Rich” and then Rich rhymes to “Hitch.” So- Richard when shortened to “Ric” which then is changed to line up with English as “Rick” is rhymed as “Dick.” Far less common Richard can also be “Hick.” This is thought to have to do in part to the difficulty/expense of writing/printing lending people to look for shorter ways to write things.