A number of reasons most of which have already been mentioned, some will I course be particularly true for those that grew up poor:
Lack of good nutrition
Lack of access to free dental care
Lack of money for toothbrushes/toothpaste
Fluoride didn't start getting added to the water until the 60's
High sugar consumption as it was cheap and filling
My own parents both full dentures by their 40's grew up poor so there was barely money for food let alone toothpaste etc! They certainly wouldn't have flossed or used mouthwash!
Dairy products were not super cheap/available
Going to the dentist was difficult as they were only open "office hours" and their parents all worked full time and then some! So annual check ups etc didn't occur they only went if severe pain/infection
Mine are a mess and need sorted, that's a combination of dental care not being prioritised at home, my own health issues (mainly mh) impacting on self care plus I was in a car accident some years ago and some of my teeth were lost/damaged through that and I'm still getting issues as a result. One of my front teeth I think has had it, it was cracked in the accident but it's now deteriorating more
Even now some families toothbrush/toothpaste may be beyond their budget it's one of the things my local food bank regularly asks for
@BungleandGeorge is also right that smoking buggers teeth too, both my parents were heavy smokers until very recently. Mum in her mid 70's now much more of their generation smoked from quite young ages
Sorry, but that was down to bad parenting I'm afraid
What a nasty and ill informed comment!
Lots of wc parents simply couldn't afford the time off work to take dc for check ups! Indeed they could have even been risking their jobs altogether and where would that have left their families?!
Firstly they are older, they've had longer to do the damage. More years of wear/erosion. More likely to be on medications that cause dry mouth, or have medical problems that lead to dry mouth/dental decay. Worsening dexterity as we age, so they struggle to maintain oral hygiene in the same way, or if they are cared for by others oral care is often very poor.
Also v true. The teeth and gums have been through more!