Are there any figures on their profitability? What are the huge costs? Shunting drivers, staffing? Paying off the rolling stock?
There are no figures on profitability,
as it has never been profitable.
The costs are high, because running trains costs a lot of money. Especially when those trains make only six one way trips per week, need detailed servicing after every one (cleaning, bed change, toilets emptying, water refilling, bar restocking), and need dozens of staff on the train for each single trip, and several locos / loco changes. All for around 200 people per trip. Compared to a day long distance train, which will carry twice as many, three times a day, with fewer staff.
The sleeper route could definitely generate some income as long you stop at all the popular destinations like Paris, Madrid, Barcelona and maybe Bordeaux? As of price yes it will probably be pricey but as long you make the train journey comfortable and maybe a bit luxurious then I’m very sure people will ride it just for the journey.
London to Madrid via Paris, Bordeaux and Barcelona is going to take the best part of 24 hours - it’s nearly 1500 miles. The only people who would use it end to end are those doing it for an ‘experience’. Many years ago I posted my estimate of how much it would cost to operate London - Barcelona via Paris, Lyon and Montepllier, taking around 12 hours assuming use of high speed lines where there is capacity for slower trains. The cheapest sleeper fares would be about £500 one way to enable break even, and it would need a long train, capable of carrying around 150-200 people each way per night, and be close to full occupancy. That is around 150-200,000 people a year, in a market of around 2m. If you can find even 0.1% of the current air passengers who would be willing to pay £500 upwards to spend 12 hours on a train rather than 2 in a plane, even if the average air fare trebled, you’ll be doing well. Let alone finding the 10% of the market you need.
Edit: yes I do use the sleepers, having used the CS several times, the Penzance, and several sleepers across Europe, Scandinavia, in the US and Australia. And like many people, barely slept on any of them.
I have also worked in the sleeper management team, albeit many years ago.