The Henrician "Device forts"

I've been looking into Early Modern history a lot more recently and in particular the dynastic squabbles between the "universalist" new monarchies of Europe. Accordingly, I've also been looking into the measures that each side took for defence, and have thus been looking into the "device forts" of Henry VIII's reign, built initially to dissuade a French attack in the era of the "battle of the spurs", where Maximilian I and the young Henry VIII routed "the flower of French knighthood". But then were later extended to further dissuade an invasion after the 1538 alliance between Valois France and Hapsburg Spain. My question is this - since most works of small and scattered fortification are usually for psycological and confidence reasons rather than absolute tactical defence, why did an intelligent man with a good administration like Henry VIII seemingly waste his money on these tiny fortresses that each had only about 30 men and a handful of cannon - not enough to provide adequate resistence to an invasion force. Moreover, Henry VIII had invaded Calais, and so there was every reason that an also martial and ambitious king such as Francis I would just repeat the French raids into the south of England like his predeccessors such as Philip VI and Charles V). Moreover, if the French had decided to come into England with the kind of armies that they managed to raise to send into Italy (such as the one they sent to the 1525 battle of Pavia which was vast) then England could only have defeated them by concentrated focuses of force and not by the kind of small defenses scattered over a large area that the "device forts" were. Henry VIII must have known of French military capibility, and surely can't have been relying on just the Italian situation and the Hapsburg-Valois rivalry to distract the larger French forces.

I suppose in this age of nearly absolute government and the rise of parliments over just aristocratic courts, a king, as you said, wouldn't want a pontential political opponent to have a castle at his disposal, especially since this was just after the wars of the roses and loyalties were still a little fickle.