Who is Jack Cade and what is the significance of his rebellion? How come we don’t hear more about him?

Great question!

Jack Cade was a fascinating character. We know almost nothing about him personally, except that he was from Kent, and that he sometimes used the name John Mortimer, which some people at the time thought suggested a claim to the throne of England through Edmund Mortimer, Earl of March, the heir presumptive to Richard II, and part of Richard Duke of York’s claim to the throne. (Another reason why some people then and now think he was working for the Yorkists.)

We do know a good deal about why Cade’s Rebellion happened because he published a manifesto in 1450 – which by itself suggests that he was either educated himself or as others have suggested that he was working with Yorkists – called “The Complaint of the Poor Commons of Kent.”

The Complaint is a fascinating look at the politics of the immediate pre-Wars of the Roses period. It’s a classic bit of “evil councilors” political rhetoric, blaming the ills of England on the fact that the king is surrounded by “insatiable, covetous, malicious persons that daily and nightly are about his highness, and daily inform him that good is evil and evil is good” and setting forth a list of grievances:

1. The evil councilors are trying to undermine the law by persuading the king that “our sovereign is above his laws to his pleasure, and he may make it and break it as he pleases, without any distinction.” The manifesto states bluntly that “the contrary is true.”
2. The evil councilors are trying to smear commoners as pro-Yorkists.
3. The evil councilors are robbing the king by advising him not to collect his normal incomes, because they’re either getting the king to give the incomes to them or to people who’ve bribed them.
4. The evil councilors won’t let anyone come before the king without paying bribes.
5. The evil councilors are falsely labelling people as traitors to take their lands and goods, while protecting real traitors whose assets should be seized to pay off the royal debt.
6. The evil councilors are corrupting the courts to the point where “the law serves of nought else in these days but for to do wrong.”
7. The evil councilors are incompetent at their jobs, such that “his false council has lost his law, his merchandise is lost, his common people is destroyed, the sea is lost, France is lost, the king himself is so set that he may not pay for his meat nor drink, and he owes more than ever any King of England ought.” (I.E, injustice and a breakdown of law and order, a declining economy and burdensome taxes, defeat in France, piracy and French raids along the English coast, and high levels of royal debt.)
8. The evil councilors are threatening to seize “gentlemen’s goods and lands in Kent and call them rioters, and traitors and the king’s enemies,” just because the Duke of Suffolk who Parliament impeached for incompetence and who the King protected, got beheaded by TOTALLY UNKNOWN PERSONS and just happened to wash up at Dover. 
9. We want everyone to know that we’re only against the evil councilors, and totally insist on everyone being tried under law.
10. We want everyone to know that we’re not going to rob anyone while we’re rebelling, honest.
11. We want the Duke of Suffolk’s supporters removed from government and replaced by the Duke of York and his followers.
12. We want the King to send a royal commission to Kent to investigate corruption.

So as you can see, the manifesto is pretty Yorkist in tone, but it’s pretty authentically rooted in complaints about the direction of public policy in 1450. And it was enough to get 5,000 men to take up arms behind Jack Cade.

Jack Cade then defeated the royal force to put down his rebellion at Sevenoaks, marched into London and declared himself Lord Mayor, and then had James Fiennes (HIgh Sherriff of Kent, Constable of Dover, Warden of the Cinque Ports, Lord HIgh Treasurer of England, Baron Saye and Sele, and a major supporter of the Duke of Suffolk) and his son in law put on trial and executed for treason. 

Unfortunately for him, Jack Cade and his men got drunk and started looting the city, at which point the people of London got sick of him, closed London Bridge against him and fought a pitched battle to hold the bridge, which caused Cade to retreat having suffered heavy casualties. Cade was then persuaded by Archbishop (and Lord Chancellor) John Kemp to disperse his army, issuing general pardons and promising to fulfill the Complaint’s demands. 

Henry VI then revoked those pardons and put a 1,000-mark reward on Cade’s head, who was tracked down and mortally wounded. His body was given a mock trial and beheaded, then quartered so that his limbs could be sent to various cities in Kent as a warning to anyone else who got ideas. 

As to why you haven’t heard more of him, he was immortalized in Shakespeare’s Henry VI, Part 2.