In this 2003 article it is said that in Germany, the time before a coffins collapse and crumble into the soil is expanding
Previously that process would take from eight to 10 years - but now in around one third of graves in Germany, it is taking longer, and bodies which were buried 30 or 40 years ago are still not decomposed.
Then an undertaker says :
"Bodies that were put into the ground 30 years ago look like they went in last week," said Walter Muller, an undertaker in Berlin. "It's like they've been pickled in preservatives and there is no explanation for it."
Other hyposthesis include "earth-born bacteria being wiped out by pollution or pesticides", or "amalgams used in dental fillings".
I found some articles related to the problematic. Apparently the process of putrefaction is supposed to take 15 to 25 years, not 8 years. Also when putrefaction does not happen it's because of Adipocere (saponification). And lack of gram bacteria could be involved.
I found no papers on the effect of pesticides or food preserver.
So, is there any proof that corpses do not decompose as well as in the good old time ? If so could the effect come from the food preservers and pesticides in our food ?
Edit: After some research, I found that :
Corpses of women, infants and overweight persons are particularly prone to adipocere transformation because they contain more body fat
So if people are getting fatter, adipocere would be more likely to happen.