A lot of women in their forties are in their prime sexually. They are often comfortable with themselves, and are happy with a casual holiday relationship.
A lot of young waiters are willing to explot their daily potential for flirtatious contact with said women - if a guy brings you a meal three times a day for a fortnight, the flirting situatiojn is already set up, it simply needs both parties to emnbark on it.
So if you factor in the numbers - thousands of women and waiters / barmen / beach sports sellers, etc., the law of averages means that relationships will grow from these encounters, some more significant than others.
The problems occur when you change the scenario. A lady of leisure looking her best, relaxed and feeling good in the sun, can be a long way from someone who gets up five days a week in rainy England to go to work, and has domestic chores to do on the weekend. A young man briming with sexual energy and happy in his environment may not be quite so attractive when he thinks that sex is all he needs to provide, and incidentals like getting a job and helping around the house don't sem to occur.
Some of these young men are from impoverished backgrounds, and cynically set out to exploit a vulnerable woman, and can change their approach when they have access to the UK and / or a fat bank account.
Of course, all this deals with stereotypes - there are plenty of exceptions, as have been outllined - but its the simple answer to the question asked.