How would you like to find out after you've closed and moved into your new home that the basement is rat-infested? You call a local pest company and discover that the sellers hired the company to treat the house for rat intrusion.
Pest infestation might not be a material fact to all buyers. A material fact is one that would affect whether or not buyers would buy a property or the price they'd be willing to pay. However, most buyers would be annoyed at the least that the sellers hadn't informed them in advance that the property had a condition that required routine maintenance. It could also make the buyers suspicious that the sellers may have withheld other information.