It's for the same reason as Maglite, Pelican, and SureFire. These manufacturers cater to the general public and professionals, not enthusiasts. Instead of having the latest and greatest, these manufacturers focus on being reliable and dependable. As such, their product development and evaluation cycles take longer time, which often results in them being a step or two behind in technology. It's also for this reason that you'll see lifetime warranties with any Maglite, Pelican, Streamlight, or SureFire product, something rarely found in enthusiast brands.
I've only gotten into Streamlights in the past couple months, and my impression of them is pretty good. Granted, they still use NiCd for their rechargeables and don't plan on going to NiMH (at least here in the USA, they are starting to use NiMH in markets where NiCd recycling is limited), but they have some interesting features. I really like the scratch-resistant plastic windows (combines the best of both: unbreakable like plastic and scratch-resistant like glass), and their electronic switches are momentary-capable and easy to press. Selecting brightness levels in the Stinger UI is one of the best implementations I've seen so far (press-and-hold to cycle high-medium-low-medium-high).