Money.
Public funded services are still cutting back, the initiatives that the various fire services have tried in the past either involved 'sharing' such as the police/hems model and really never lasted beyond trial periods, or being frightened off when the true cost of running a specialist fire helicopter unit became clear. Having something the size of a puma on standby at a location near enough to make a difference (for Eastbourne pier at least) would soon be chopped when the next round of cuts were discussed.