Monday to Friday period takes 5/7 of the week, so the probability for the contest to take place in that period is much higher. You do the math.

It would be nice to have more contests on weekends. The contests are held at pretty busy hours for us in North America.

Yeah your'e right man but I rather relax on week-end than participate to the contest. Also it depends on your time zone whether your'e able to participate or not, for example 90% of the rounds dont overlap with my clases (Thats of course for Romania) , and I also think many of the Div1-s happen durring the weekend already.

Yes, Codeforces contests are often at inconvenient times, but you can't assume Codeforces will schedule all contests to be to your schedule. Time zone will affect things (Russians will do contests at 7:30 PM, and I'll be doing them at 10:30 AM), and dates as well, but for me, at least, weekends are very bad. If all the contests were on weekends, then what about me?

I think Codeforces introduces enough variety (albeit not enough to my liking), the schedule is quite varied. There are Sunday contests, Monday contests, Tuesday, Friday (bah Friday; I can't ever do 10:30 on Friday). They jump all over the map.

You can't hope that Codeforces will conform its contests to your schedule, not to mention that everyone's schedules, let alone time zones, are different. Yes, maybe a majority of them are in the weekdays, but there's enough variety for you to attend some, I'm sure.