Wether senders send e-mails very frequently, recipients might feel that they are being inconsiderate towards them an the work they are doing at the time. Therefore, they “charge extra” by not paying attention to those messages.
Remember also that senders positioned as people that permanently send chains, jokes, accusations, or messages to cover their backs and/or justify themselves also have a high cost in the attention of recipients, and they are also perceived as inconsiderate.
In the long run, these practices only deteriorate the reputation of senders, and recipients end up thinking that it isn’t worth investing time in those messages, erasing them without reading them.
Some people write messages that are extremely dense and difficult to understand, and it is difficult for their recipients to pay attention to those messages. These are the cases where the recipient got more work, having to phone sender to get the message quicklier, and saving time “digesting” the information.