You remind me of another Spanish poster here. Maybe what Spain did was more important. However, France's army and fleet were decisive at Yorktown, so that gets more press. Most of what Spain did was covert, sending money and supplies. The fighting in Florida, the west, and at sea mostly didn't have much to do with helping the rebelling colonies.
Britain had an Empire to run and supply and an Empire's enemies, they had pressures from all quarters from numerous nations.
Fundamentally it was a culmination of all the help either directly or non-directly that the Americans received which didn't allow Britain to focus on keeping America.
In fact I think its overplayed on how much Britain actually prioritised wanting to keep America, I think history shows that most of Britain's preoccupation with America was to stop France taking control of it, the Americans were viewed as a British colony, letting some rebellious British foreign subjects keep an "outpost" which needed farming, colonizing, expansion, investment and fortifying, wasn't something the Brits were ever going to have the man power to do directly from the Crown's resources and so letting them have it was not as nearly as much of an issue as France controlling it.
Once it was clear America could protect its interests from foreign powers like Spain, Britain was laid back on letting it go in comparison to other concerns.