I have not kept exact tabs on this, but there is a pattern to the type of advertisements featuring celebrities.
Adverts for something real that you can judge on its own merits like mass market cars, furniture or white goods, tend not to feature celebrities. You can test drive a car, decide whether you like the styling, compare its fuel economy and so on. You can test sit on a sofa and decide whether it's comfy or not.
There's a good list of the reasons why advertisers use celebrities here, but it is just as interesting to look at the type of products they are used for and work backwards from that.
Celebrities tend to appear in adverts for the following, in no particular order:
1. Supermarkets, which are essentially all the same, they sell the same products for the same prices in the same way. So they try to differentiate themselves by using celebrities, apart from Aldi and Lidl which mainly compete on price, so their adverts just compare prices for their own brand goods with similar branded products. This also applies to Littlewoods and Very.
2. Luxury items/conspicuous consumption like really expensive watches, which don't tell the time any better than a £15 Casio. In fact, even a Casio is superfluous if you are carrying a mobile phone.
3. Lifestyle things/conspicuous consumption which serve no useful purpose especially perfume, which all seem to follow exactly the same template and are incredibly dull. In contrast to mass market cars, luxury car makers are far more likely to use celebrities/racing drivers. The same goes for fitness paraphernalia like Kate Hudson/Fabletics, these ghastly fitness trackers and gym memberships. People buy sportswear in the vague hope it will encourage them to actually go jogging etc but usually never do. I'm pretty sure that ninety percent of all fitness gear is only used once or twice.
4. Generic white label products like price comparison/estate agent and gambling websites, where one price comparison/estate agent or gambling website is the same as any other, what these sites needs is some sort of critical mass of users especially price comparison websites, if you are number one, then everybody wants to advertise with you, if you are number two or three then far fewer people will advertise with you.
5. Things which are cheap to produce but can be sold for prices that include a lot of rent, like replica football kits, which the teams advertise for free each time their match is broadcast. This also applies to chocolate, as much as I love chocolate every now and then, it all tastes the same to me.
6. Cable television and mobile phones. Companies which have their own content (Netflix, Sky) can advertise their programmes; BT, EE, Virgin etc do not have own content so it uses celebrities.
I can't quite boil that down to one common theme. To be mundane about it, it's about product differentiation or creating a demand for what is a perceived value-added service rather than the product itself.
The joker in the pack is Gary Lineker advertising Walker's Crisps, which are pretty much the best crisps for the price if you buy multipacks in the supermarket. You can judge them on their merits and either you like them or you don't, so why on earth they pay Gary Lineker or Paddy McGuinness a fortune to get on everybody's nerves is a mystery to me. Those adverts are truly awful and always have been. Coca Cola does a lot of advertising, but by and large they don't use celebrities and their adverts are usually pretty good.