To understand how we got to where we're at, you need to crack some books.
The best is Yale law professor Akhil Reed Amar's "The Bill Of Rights" (1998), which shows how the various elements of the Bill Of Rights were supposed to change under the 14th Amendment. Amar is no friend of the RKBA yet his own research forced him to come out on our side - very unwillingly!
The short form is this: the 14th Amendment was supposed to apply the entire BoR to the states as limitations on them, in 1868 upon it's passage (and yeah, it passed - at gunpoint where the South was concerned but they had it coming).
It didn't work out that way because in a series of cases between 1872 and roughly 1900, the US Supreme Court simply trashed the 14th from top to bottom, leaving it more or less completely useless. The cases involved start with Slaughter-House (1872) and run through Plessy v. Fergusen (the infamous "separate but equal" case of 1898). The worst though in my opinion was US v. Cruikshank, officially an 1875 case but the final decision came out in 1876. Charles Lane wrote a whole book on that case and it's aftermath, "The Day Freedom Died" (2008) which was cited favorably in Heller. Cruikshank directly caused at least 4,000 lynchings and uncountable numbers of other civil rights violations when it took the federal government out of the civil rights protection biz.
In the 20th century the Supremes realized they went too far. They rebuilt the 14th Amendment "crooked" - one piece at a time they applied the Bill Of Rights to the states under the theory of "selective incorporation", in which aspects of the BoR were declared "fundamental to due process" and selectively "incorporated" (or read that as "applied") to the states.
The last such selective incorporation case applied the 2A to the states in McDonald (2010). At the McDonald hearings, Alan Gura and company tried to get the court to finally ditch the "selective incorporation" fraud that began in 1872 in favor of "full incorporation under the Privileges and Immunities clause" (of the 14th Amendment). This would have had a bunch of other effects:
* It would have forced the states to use grand juries for major indictments, as that's one piece of the BoR not yet "incorporated".
* Ditto for the "quartering of troops" thing (3rd Amendment) which nobody really cares about these days.
* It would have required state and local trials in at least moderately serious civil cases to have a jury option.
* It would have also protected other civil rights not listed in the BoR, including a right to "free travel without pass or passport" (mentioned as a "privilege or immunity of US citizenship" in Dred Scott - which listed civil rights blacks didn't have as of 1856). And another really big one: a right to marry who you wanted. Yes, this would probably be read today to include gay marriage, which is likely why the NRA argued against "full incorporation" at the McDonald orals in favor of maintaining the fraud that is "selective incorporation".
* There are probably economic rights inherent as "privileges or immunities" that today are being stomped flat by grossly improper applications of eminent domain and other such lunacy.
So. This history is why there's no state requirement for grand juries. It means that some states don't have truly functional grand juries at all (California!) and hence fraud runs rampant that might otherwise be caught. It's also why a lot of traffic courts have switched to being "civil courts" so as to deny you a host of criminal law protections.
It's because of fraud going back to 1872 and still not addressed.