Why did people used to overcook vegetables?

Another reference in literature to this issue can be found in Jane Austen’s Emma.

Remember Mr. Woodhouse and his hypochondria and overconcern with health and eating and indigestion? At one point some asparagus is brought to the table cooked thoroughly enough for his other guests, but he found it too underdone and sent it back for more cooking. At another point he is advising his supper guests to avoid indigestion by limiting themselves to a very lightly boiled egg and to avoid the muffins.