They never see it because its equipment and its people are currently employed full time in the fight against ISIS in Syria and Iraq. When people people are at home they need a break.
And that there opens up another question, if indeed the fleets of everything are so tied up fighting a couple of "minor" wars, that they cannot attend airshows to show the British public where their hard earned cash is going, what happens when we have a full blown one on our own doorstep, if you have no spare capacity in your fleets for those theoretical eventualities, you are fooked, it also begs the question are the UK defences so depleted while these "minor" wars are on going that they are stretched and incapable of putting up an effective defence?....
Incidentally the NHS do roadshows etc