There is quite a lot to answer here.
1. To get from Swanage to Wareham the operator, who ever it is, has to operate on network rail metals from Worgret Junction to Wareham. This means the operator has to meet mainline standards which includes (1) public liability insurance of £155M (I think) which is expensive especially when divided over a relatively small number of passengers (2) drivers have to pass the mainline medical and possess the European Rail Driving Licence (3) the rolling stock has to meet mainline standards which effectively means meeting modern crashworthiness standards, central door locking, having various bits of electronic kit including Train Warning Protection System and the kit that tells the controller where the train is, which direction it is travelling in, the speed etc. Toilets have to be tanked ie effluent goes in a tank not on the track. All these standards go to safety of passengers, rail workers and the general public. Some derogations are available but not for everything. The issues with the Jacobite do not exactly encourage ORR to grant derogations.
2. The operator has to pay track access charges (which helps pay for line and infrastructure upkeep) and station access charges (which pays for station upkeep).
3. Scheduled service operators have to meet various commitments including offering delay repay, access for mobility impaired passengers and having an agreed complaints handling policy. They also have to sign up to common ticketing standards and ticketing agreements including accepting railcards etc. These common standards are for the benefit of consumers. (How would it be if for example child fares applied at different ages on different operators services?)
4. The South West Mainline - Weymouth - London Waterloo - is very busy. Any delay can have a massive ripple effect all the way to London. Hence SWR and others need to be confident that any other operator will not create a disproportionate number of problems.
5, When operating the Wareham service the signaller at Corfe Castle (the main box for Swanage Railway) has to be fully trained for handling the additional complexity introduced by the Wareham service. Some volunteers do not want this additional responsibility and so have opted out of the additional training required and thus wont be rostered for those days.
All this compliance for safety and customer benefit comes at a cost. The smaller the operator the greater the cost on a per passenger basis.
Swanage Railway would like its own licence (or at least it did prior to this summer - its view may have changed) so it can utilise its own volunteer drivers subject of course to them meeting the required standards etc. Whilst they may be able to find and train sufficient volunteers for a 60 / 90 day one shift operation, a 363 day 2 shift operation is of a very different magnitude.
No one doubts that having a summer tourist service between Wareham and Swanage is of some benefit. The "problem"seems to be that the costs outweigh the revenue. So a subsidy is required but the questions arise: (1) does the subsidy represent good value for money (2) should govt subsidise this when another form of public transport is already subsidised - the bus.
Running a year round service daily with services from say 07:00 - 1900 will require a great deal of subsidy. One view -which has some support - is that the demand is too low to justify the level of subsidy required and again these monies could be better spent on other transport projects for example again enhancing / supporting the bus service.
