The airlines are stuggling to remain profitable in these tough economic times, and the latest measure they have taken is raising the fees on checked bags. In times past, you could check one bag for free with most airlines, but not anymore.
For some travelers it simply is not possible to "travel light", but if you can get by with just a small carry-on bag you now can save a pretty good chunk of change. If you simply must take along more items than you can fit into a carry-on, try to limit yourself to checking just one bag if at all possible.