It is just hard to overstate how lame John was. (There are some historians, like the one that compiled my handy royal anecdotes book, who try to rehabilitate his rep, and to those people I say, more or less, Pfft.) Let's start with this:
And that's what he had at the end of it.
Sure, it's not like he lost everything in France, but it was a lot. Moreover, it was most of his mother's inheritance of Aquitaine and Poitou; it was the homeland of the Plantagenet dynasty, Anjou; and it was freaking Normandy, which had been cheek-by-jowl with England since the Conquest. And he didn't lose it all just because of a lack of military prowess; sure, he got the nickname "Softsword," but he also showed flashes of military . . . competence. He won, like, this one battle once? It was pretty good. But anyway, the problem was not so much that he lost a bunch of battles as it was that so many of his subjects rose against him (and allied with the King of France) in the first place. Because they hated him.
Take the people of Brittany, for instance, who preferred the claim of John's nephew Arthur, who was also their duke. They didn't like John much to begin with--and less so once he probably murdered Arthur. Or take many, many of his continental nobles who turned against John when, instead of ransoming the prisoners he took at his big victory at Mirebeau or putting them under honorable house arrest, he put them in chains in dungeons. Or, of course, take the barons in England who, chafing against John's military failures and abuses of power, were like "NO DUDE SERIOUSLY. STOP IT" and forced him to sign the Magna Carta in 1215. John saw the famous document less as a foundation for Western government in future centuries and more as an annoying treaty he preferred to ignore.
This is not even to mention John's lust-driven second marriage to a twelve-year-old girl. (Ew.) We also haven't delved into disastrous feud with Pope Innocent III. You see, the Pope wanted one guy to be Archbishop of Canterbury, and John wanted a different guy. Things escalated and eventually resulted in the King's excommunication and an interdict on his kingdom. Interdicts were bad times, yo.
Therefore the king withdrew fromm the negotiations and so did the bishops and everyone else and, on 24 March by papal mandate, divine services were suspended throughout England. Great sorrow and anxiety spread throughout the country. Neither Good Friday nor Easter Sunday could be celebrated, but an unheard-of silence was imposed on all the clergy and monks by laymen. The bodies of the dead, whether of the ordinary fold or the religious [that is, not-monks/not-nuns vs. monks/nuns], could not be buried in consecrated cemeteries, but only in vile and profane places.
The king ordered the few monks who remained at Canterbuy, the blind and crippled, also to be expelled, and the monks to be regarded as public enemies. Some fled England, some were imprisoned, some were saved by money, others suffered many afflictions; their woods were cut down and their men were fined and taxed heavily. The whole of England suffered this burden. The people were forced to pay at first a quarter of their money, then a third, then a half. Even the rents of the cardinals and whatever they had in England were taken away from them and Peter's Pence, which the Roman Church had had since the time of Cnut, were withheld by the king. . . . Therefore the rich and poor left England, countless men and women; theirs was a thankless pilgrimage to avoid the enormous cruelty of the king rather than a devoted one.Ralph, abbot of Coggeshall; via The Plantagenet Chronicles, ed. Elizabeth Hallam