Part of this difference is caused by the difference in the time that a THS listing is active. In the UK that is much longer than in France.
Yes, that difference is also caused by the difference in where members are. More Brits that apply for sits in France than the other way around.
Fast solution: Mayfair Equities should try to buy Nomador too 
A better way to see what the imbalance is:
- There are “10000” house and pet sitters from England, United Kingdom
- There are 9962 house and pet sitters from England, United Kingdom with at least one review
- There are 3828 house and pet sitters from Germany
- There are 1983 house and pet sitters from Germany with reviews
- There are 2377 house and pet sitters from Spain
- There are 1851 house and pet sitters from France
- There are 1609 house and pet sitters from the Netherlands
- There are 1222 house and pet sitters from Scotland, United Kingdom
- There are 1100 house and pet sitters from Ireland
- There are 884 house and pet sitters from Italy
- There are 746 house and pet sitters from Switzerland
- There are 477 house and pet sitters from Belgium
- There are 473 house and pet sitters from Wales, United Kingdom
- There are 364 house and pet sitters from Austria
- There are 266 house and pet sitters from Denmark
- There are 259 house and pet sitters from Sweden