It's worth bearing in mind that "furlough" in the UK is not the same as in the USA.
In the UK, the furloughed person remains employed by the employer and is therefore on their headcount (and their financial costs) - the employer is simply receiving money from the government because the employer has no work for the employee right now. If the employer was to employ more people while furloughing some others, the total employee headcount would rise and when the furlough period ended the employer would have to pay salaries for all these people.
In the USA (particularly in the airline industry), a person furloughed is no longer employed. They are no longer on the company headcount, nor is the employer considered to have them included in the staff costs. The employer agrees (usually as part of a union bargaining agreement) to offer re-employment to the furloughed former staff before any other people, hence the use of the word "recall".
The current "furlough" in the UK is a recent idea for the UK - while common in Europe, especially in Germany, it's a new thing for the UK. Furlough in the USA is a long-established practice in many industries with highly cyclic employment, such as aviation and vehicle manufacturing.