I like hot cross buns at any time of year, because I like sweet yeasted breads. I also believe in eating things in season, even if the season is an odd stew of cultural and religious traditions rather than, say, the planting calendar. And Good Friday, the traditional day to eat hot cross buns, mixes them all, as research I did about 10 years ago revealed.
I started with the Catholic Encyclopedia entry on Lent, which of course confirms that eggs and butter, central ingredients of hot cross buns, are traditionally given up during Lent—hence pancakes on Mardi Gras, called Fat Tuesday because of the imperative to use up butter and eggs before the fast. And the profusion of eggs at Easter, both dyed and in breads, is a way to use quickly the eggs chickens keep laying even during Lent.
So why do hot cross buns start appearing in bakeries on Ash Wednesday, the first day of Lent? The answer is, they shouldn't. It's a way for bakers to stretch out the season. Less odd, but still odd, is that they should be associated with Good Friday, the holiest and most somber day of the Christian year, itself a fast day with one full meal, meatless, and two much smaller ones.
Some answers appeared in a 1994 Washington Post article by the late Geoffrey W. Fielding, and English expat who settled in Baltimore (his obituary here), which gives a longer version of the history our own Jennifer Ward Barber engagingly recounts in her post on hot cross buns. Like most writers on English breads (and Jen!), Fielding drew on Elizabeth David's English Bread and Yeast Cookery, and also a 1989 history I haven't seen by Lizzie Boyd, British Cookery.