Really common practice here in the UK, especially with big sites where a contract is going to be 20+ trucks. They will happily put the machines in at a loss to get a foot in the door and try to rely on a high residual value on the machines at the end of the contract to make the money back (normally ends badly due to abusive drivers/high hours).

It's been going on for 20-30 years and is in my opinion very short sighted practice. Here it has completely knocked the profit out of renting as they have all collectively spent too many years running around cutting each others throats instead of maintaining a 'fair' market price which benefits all, i.e the forklift companies make a healthy profit meaning there's money around to deliver a better service to the end user to keep them happier, and potentially higher wages for engineers which would keep us happier and hopefully attract some new skilled talent to the industry.

It's bonkers when I can rent £15k forklift for £80-95 (£100 short term) a week but if I go to a tool hire shop I'll pay £50 a week to hire an SDS Max hammer drill which I can buy new for £500.

I also do LOTS of work for other lift companies who have long distance contracts and it is frustrating, you can't do your proper job because the other forklift company won't pay the bill and the customers generally unhappy because you can't fix his small issues there an then.
As triumphrider said all you can do is explain its out of your control, it isn't your customer at the end of the day, and other forktruck companies are the WORST customers to do work for in my experience! They don't miss a trick ;)