This is an interesting subject and perhaps I can comment further
It all comes down to two fundamentals: risk and reliability. In general, heritage railways operate in an environment where both of these are low when compared to the Big Railway (which we shall call 'BR' for some strange reason).
Risk.
Heritage railways operate in the world of funny money. Labour is mostly free and the operating costs of the locomotives, units or rolling stock seldom reflect the true costs of operation and maintenance. The same applies to the infrastructure. Now, to an extent the railway can get away with that provided everything goes in the right direction: certainly running DMUs that are kind to the track and are relatively easy to maintain leads to a benign environment. However, if the degree of operation becomes too great, exactly the same issues as BR start to emerge and the risk to the business increases disproportionately.
Hand-in hand with this is the staff risk: as we have found at the EVR, running (relatively) intense services day in, day out, causes stress on a pool of a nominally free but finite resource. Add to that the prospect of doing this at 05:30 on a wet Tuesday in February and the risk becomes too high. The only way to mitigate against that is to hire paid drivers and then you're dealing with significant amounts of real, not funny, money.
Reliability
Reliability operates hand-in-hand with this. Heritage railway operate mostly life-expired stock and seldom have the resilience in numbers to provide a spare if the train fails. Guaranteed reliability costs real money, as would having a fitter available for that wet Tuesday.
Then we come to the customer: cancelling a train when operating a pure heritage service is inconvenient but seldom causes the passenger real grief. Do that or run late when the passenger misses their connection on the main line and you will lose their business very quickly.
Other factors
I have been tempted to propose something like a commuter-type service on the EVR but other factors beyond risk and reliability come into play.
Our trains connect with the EMT service from Matlock to Derby and Nottingham, so why not connect with the morning and evening peak trains? The evening service would be a doddle in the summer: all we would have to do is run one extra train in the late afternoon, but the morning service would be beset with the problems above, while there's a very simple issue for normal train users. I travel to Nottingham on occasion and catch a train from Cromford, the nearest BR station to Wirksworth. I can get a table to myself, whereas if I boarded at Duffield, the train wold be full and standing. Would a 'normal' be bothered with the hassle?
Another option might be 'snow-buster' services if the weather gets really bad. Well, this is a possibility but (1) who knows if and when we might get snowfall sufficiently bad to close the road to Wirksworth and (2) how would our traincrew volunteers get to Wirksworth to take-out the train?
In conclusion, it's a lovely idea and in the summer I am proud that one can get a connecting service from anywhere in the UK through to Wirksworth with just a couple of changes. However, taking-on a true, completely reliable service is way too risky for pretty well any heritage railway.