As a regular on the Fylde Lines, I am shocked that you think the South Fylde Line (Preston - Blackpool South) has "very few passengers". The line has a clockface timetable running every 60 minutes, seven days a week in the summer. Based on data for tickets sales (which really can't be relied upon as considerable amounts of people use Blackpool North tickets) - I'd estimate very roughly that around 650,000-700,000 people used the route in the financial year period 2009/10. I'd say Ormskirk is not close to that.
This isn't comparable to the Ormskirk branch, which operates with just a single 153 most of the time. Busy 142s are the norm on the South Fylde Line.
The trains are very well loaded at peak times Monday - Friday and can become overcrowded on the weekends due to additional tourist traffic. It sees significant use from St. Annes and Lytham to Preston for commuting and leisure traffic. A lot of people use it to go to work or education.
In the year 2008 – 2009, 112,000 people used the Blackpool South railway station which is an increase of around 7,000 on the previous year and a significant increase on 2004 – 2005 when only 82,804 people used the railway station. St. Annes-On-Sea served 121,938 passengers in the same period, with Lytham serving 71,000.
Let's compare this to Ormskirk Line: most passengers using Ormskirk station are using Merseyrail Electrics, so the busiest intermediate station is Burscough Junction which saw just over 40,000 people in 2008-09. Not much compared to say, St. Annes?
There is a lot of suppressed demand on the South Fylde Line, it has the potential to be far busier with a passing loop and more frequent service to say, Manchester Victoria.
So, absolutely not is the answer to your question. Try the South Fylde Line on a Saturday Morning, it's often packed with shoppers (note: not tourists) going from St. Annes / Lytham to Preston. Equally, the Pleasure Beach has masses of passengers on those days. All this combined, makes some very busy trains!