before something happens that will cause everyone to ask "why were we stretching ourselves so much for a publicity event?"
... because it is not a publicity event.
The (out of date by nearly two years) GAI2022 mandates by the Air Force Board who is to hold airshows and why. The party line is to 'Educate the general public in the Defence Mission of the UK', with recruitment and service charity fundraising both worthy by-products.
In short: Dear taxpayer, please come along and I will show you what the Defence Budget (your tax) pays for. The air show organisers pay a lot of money for RAF participation and such events are financially self sustaining.