beemerphile1 you beat me to the explanation. I think the low current flow of LED lights also leads to the dirt problem also. I find I'm popping batteries and rubbing the contacts on my jeans often. The bigger problem I have seen with LED lights is I have them everywhere, therefore I never/seldom use up a battery, they do last forever and the batteries go past their use date and start leaking. Not a problem on the free/cheap ones but when it happens to one of my good ones.... So I try to remember to pop out batteries on a regular bases to check the date on the batteries.
I have several favorites but none that were super expensive. I have a 3 D cell unit I got on sale at HomeD a couple of years ago for $25 that is the brightest flashlight I have ever owned., 1000+ lumens, it lights up the night. I have a couple pocket flashlights that were in the $10 range, on sale, that I like a lot one is a Coast. I find they make a flashlight that feels and work enough better than the free ones that I will grab them first. Also have a few Maglites in different sized from AAA to D. Oh I also have some head lamps, 3 cheap one slightly better with focused beam.
Boy I have a lot of flash lights :-)