When he arrived in London in 1712, Queen Anne awarded him an annual pension of £200, the equivalent of £25000 today, which George 1 continued. This was a respectable income, and he received a varying salary from the Royal Academy, but he died a rich man in 1759 with £17,500 in 3% annuities at the Bank of England, just under £2.2 million at today’s prices.
His salary from the Royal Academy was sometimes not paid and the Academy ran out of funds in 1728. He owned shares in the South Sea Company, the infamous “Bubble”.
In 1732 the Bank of England’s records show that he had £2300. In the subsequent seven years he made no deposits and made withdrawals each year until he closed his account in 1739.
He suffered a stroke in 1737, was involved in a coach crash in 1750 and had cataracts and eventually went blind after a botched eye operation 1751.
He pre-dated the invention of the gramophone, which according to Tim Harford in 50 Things That Made The Modern Economy created the trigger for capturing the value of music. https://www.bbc.co.uk/programmes/p04x6xg6
The answer is to be found in some detailed research from a visiting academic at the Bank of England. https://bankunderground.co.uk/2019/11/08/handel-and-the-bank-of-england/
Essentially he was at the forefront of a change in musical taste. The public had lost interest in opera but their interest in English Oratorio was emerging. Baroque house music?