It doesn't even need much additional resource to improve it though - just shuttle the unit back and forth Doncaster to Lincoln, it has a journey time of 50 minutes so with 1 unit you could provide a 2 hourly clockface service from both ends and you still have a timetable which is an improvement on the service we have at the moment. OK, there's the cost of crew and extra unit mileage but it doesn't require any additional units which is the most scarce resource.
As
ChiefPlanner has mentioned the whole timetable in Lincolnshire is resource led. The services between Lincoln and Doncaster are only run in marginal time where the units are not utilised for anything else.
A case in point from examining the weekday timetable is there are 2x services within an hour during the evening - both originating from Sleaford. These particular services would otherwise go to Peterborough via Spalding in the daytime. But as that route (also set in aspic) doesn't serve passengers between Sleaford and Spalding after 16:30 the units can be used for Doncaster instead.
The other 3x services to Doncaster are running in gaps where the unit would otherwise be sat in a bay platform at Lincoln, as that unit is used for peak time strengthening in the morning and, again in principle by freeing up another unit in the area, the same again in the afternoon.
At present no service in Lincolnshire is specified by the government (or any previous ones!) to be 'customer' led. The timetable requirements are all about providing a 'reasonable' service across much of the day, delivered with the
minimum amount of resources.
Of course
TheBigD is correct in pointing out that in the next franchise, many of the routes radiating out of Lincoln will see vast improvements. But that will be expensive and will be subsidised accordingly. I would doubt that the increase in collected fares would go anywhere towards meeting it otherwise.
Something to note is if there genuinely was the potential passenger numbers to support such an uplift in services and costs, then the private sector would of delivered it years ago.