Flight training is expensive because you start off in an aircraft that costs pushing UK£ 60 per hour in fuel alone, never mind the eye watering costs of maintenance using approved organisations and replacement part prices that beggar belief, with an instructor who is not only trying to recoup some of the costs of his/her commercial training but also the additional costs of the instructor rating. Landing fees, handling charges, club membership, medical, security badge charges and so on just rub salt into the wound.
If you think that is expensive, just wait till you get into the realms of multi-engine and instrument training.
All of the foregoing is as cheap as chips compared to type rating costs.
The cost is the only real filter, no great intellectual capability or application is required, but, astonishing as it may seem, enough people find the funds for the system to churn out more pilots every year than the industry requires. As has been observed, the last time the UK had a shortage of pilots was in 1940.
With that background, why on earth should the taxpayer give flight training any kind of subsidy? Its clearly not needed to meet the industry's needs, and as long as a lot more people are doing it than can reasonably be expected to gain employment from it then its understandable if its regarded as a hobby and taxed accordingly.