Seeing as I download my TV, I don't really much care. But as far as why... because they're gambling long-term success for short-term gain. It's the reason why Invasion was cancelled: they took a solid show and stuck it up against some behemoth in the hopes of unseating the current winner for that timeslot, despite the fact that it was blatantly obvious that they woudn't win. They just want to inconvenience the other network, and if a good show dies in the process, "oh well, it was too good and next season the producers would have had justification to up the budget."
The Bottom Line is what makes network TV tick. Fortunately it's not ALWAYS that way with cable TV, or if it is it's to a lesser extent. Cable: the last haven of good TV. (amid a lot of syndicated reruns)