The reason that there is such a low average lifespan for French Bulldogs is not quite so obvious as the breathing issues/joint issues etc..
And it might surprise people to know that the short nose isn't the biggest cause of their breathing issues either - it is actually the short neck!
(Obviously, the short nose and pinched nares are still an issue, but the short neck has a bigger impact!).
The reason is that French Bulldogs are SO hugely popular there are a truly incredible number produced from awful puppy farmers, imported illegally too young from eastern europe, bred from horribly unhealthy parents... etc.
This means a really large number die as puppies from infections and illness, they die in the first year or so of life, they die in surgery, they die very young from heat stroke because owners still don't take it seriously...
A 'healthy' one from a good breeder (there are some around), with a responsible owner (mm) who will seek professional advice on whether they need a BOAS op or not... who keeps the dog lean and fit and manages them really carefully... will typically see their dogs live to 10+ or even 12+
But there are SO many who don't fall into that category, who buy frenchies on a whim or who are breeding them as a get rich quick scheme.. those deaths are skewing the numbers.
The listed average age for French bulldogs is 10 - 12 years - but those figures were arrived at some years ago, before the current FB population explosion.
If you look at the average lifespan for similar build/noses - both Pekes and Pugs have LONGER average lifespans (12-14)... again, they haven't seen the population explosion that FB's have... neither is 'more' healthy, they're both pretty awful conformation wise!
I still wouldn't buy one, and even the 'good' ones that owners swear down do not snore or snuffle, can be seen having to breath through their mouths because they can't breath through their noses, and are seen frequently choosing a propped up on the back position unlike other breeds (loads of breeds will sleep on their backs but very few will do so propped up like a human dozing in front of the sofa, in the corner of a chair) because they still struggle to get as much oxygen in as a longer necked, longer nosed breed.