Because they last too long. No, seriously. If I put a 25,000-hour light in a typical fixture (4 hours a day) that’s 17 years until I replace it. Am I going to be around in this house to see if the claims pan out? And even if the light does last that long, why should I buy one now when in a couple of years it will cost half or a quarter the price? Early adopters always get screwed, but the longer the life of the product the worse they get it. An LED light is pretty much a lifetime investment, so the sooner you switch over, the more you pay.
Which is why even early adopters are having a hard time justifying them. Which is why, in turn, the prices aren’t dropping as fast as they otherwise might. Chicken, meet egg.
There are the power savings, but. Let’s say I replace that 60-watt bulb with a 6-watt LED. 54 watts at 15 cents a kilowatt-hour means about three and a quarter cents a day in savings for my 4-hour-a-day light. Payback time: about 3 years. Meanwhile, if I get a compact fluorescent for $5 or so, it might use more than twice as much electricity, but the payback time is more like six months. Sure, I’ll have to buy another in 5 years instead of 15, but both kinds will be even cheaper by then.
So this leaves the early adopters with longer time horizons (If I were building a house I’d probably go with LED fixtures) and the people who have money to burn in a good cause. Enough? Or not enough?