Just in case you hadn't noticed, Slim20, there already is a major international airport with direct daily intercontinental services less than an hour's drive along the motorway from Liverpool.
That's not Liverpool airport's market, and probably never will be. Liverpool has found a very fruitful niche with "lo-cost" operators and short to medium-haul freight .
This success story at Liverpool means that the population of the North-West (and beyond) now has extremely good access to a huge global route network served by a wide variety of airlines.
No other region of the UK is so well-served.