The 8th Amendment prohibits "cruel and unusual" punishments, not disproportionate ones (although some Warren-era Supreme Court cases did add the concept of disproportion to the 8th Amendment). In the Founders' day, shoplifting and pocket-picking were routnely punished with death.
The intent of the amendment is both to enforce the presumption of innocence until guilt has been proven, as well as to permit an accused the freedom to prepare an adequate defense.
What does any of that have to do with "cruel and unusual punishments"? Unless you skipped sometyhing and have gone on to talk about the bail clause of the 8th Amendment.
shoplifting and pocket-picking were routinely punished with deaththat would be cruel, because, as everyone knows, people only steal because they're hungry and/or oppressed. /sarc