HH
There are many answers to your question.
You could equally ask why we have a tank regiment but virtually no tanks.
An Air Force that cannot operate fully on its own and has few aircraft
Why we bothered to have military SAR doing a civilian job.......but not able to do CSAR.
The list goes on
Back to the paras. We don't train significant numbers of men to parachute and haven't done for some years.
Paras drop out of range of HMGs on the back of a pick up, and usually out of sight of man pads at the target area. A c130 can fly faster, further and in weather that would ground a chopper.
There there is the mental advantage that arduous training brings to a soldier. The actual parachute component is often considered the easiest part of the training, while the physical part of P company is considered the hardest.
The extra boost P company and being para qualified brings to a soldier is often of help in battle or stressful conditions. Paras often consider themselves an elite and a lovely remark to emphasise this was a remark made by an officer from the green devils (German ww2 paras) about the Red Devils (Brits) when he said there were no 'mummies boys' in the Red Devils.
The list of 'wasted training money' is almost endless really. Can a Typhoon pilot control his/her aircraft better if they have had lessons in use of cutlery or mess tradition?
Right, sorry for all that waffle, but the next question has to be what is is the use of para training rock apes........ If any area is well defended against para attack it's an airfield