This is a good question.

It changed because the statement people hung the flag for decades is entirely recent history. Anyone over 50 knows it is not the case,

It is true of the union jack. Although since Victorian times not hugely so and often seen as tacky. But the St Georges flag dropped from use before the 1980s.

The reason is pretty clear. From about the mid 1800 most major English political parties have been unionist. It is a part of the Tory party name. But all 3 major parties and most smaller parties in England have been unionist.

We have no major England separation party. Whereas the other 3 nations all have such parties. Calls for England as an independent nation. Have never had a majority following.

As such the flag of England dropped out of use in the mid 1800s. As the main parties were successfully pushing the Union Jack as the main flag for England. In an attempt to diminish the separation parties of other nations. And no vocal group in the nation of England was opposing the lose.

As such when the National Front. Then BNP etc etc started to use the St Georges flag as a call to remove all non white from the UK. Opposition was very much directed at the ideals. Not the use of a flag few felt a link to.