It's not only happening in UK or US as well.
I'm from Lithuania and whenever I want to watch my domestic basketball league or any game broadcasted on our domestic channels I get just spammed with gambling ads, it's like there's no other type of ad. It's gotten to absurd levels in the last few years.
To exploit the freshness of the situation for ratings/clicks.
Most people in media are heartless bastards that will stoop to ridiculous lows to get ahead.