Only because you don't like the color, or maybe the texture of dirt? We wash off dirt because it's dirty, and dirty things aren't good for us (because of bacteria...).
Also because gritty lettuce makes a salad I don't eat. Spinach is the worst . . . plus it seems to have Listeria from time to time . . . 3.2 second wash minimum
Err, your immune system can cope with a bit of bacteria. But if you don't wash your salad and get a massive load into yourself, your body will deal with it by extorting everything in your stomach. E.g. you'll puke the entire night. You're welcome.
When you rinse salad with water you are not cleaning a significant amount of bacteria off it. You're getting soil and bugs.
Unless your salad is contaminated with something, not washing it will at worst be gritty and unpleasant. It won't make you ill. If it does, washing it will make no difference.
I don't think that salad bought in a store should have bugs and dirt on it, if you find them in your sink when you wash it you should change supermarket
EDIT:
My bad, I was thinking about pre packaged salad, not like a whole head of lettuce, OP is correct and OOP should wash their lettuce better
I've been using Original Commenter (OC) to talk about the person who starts a comment thread. Seems to be pretty intuitive. Wonder what the acronym would be for commenters responding to OC and starting different comment branches. Probably makes sense to just use their name
You might be thinking of pre-packaged salad which, while already washed, can still contain bacteria. But if you’re buying plain lettuce, it’s absolutely not pre-washed.
They're definitely washed after being harvested, but as someone who has seen how it's stored between that and the store shelves, I'll give it a rinse every time.
Lettuce grows in a bundle of very tightly packed leaves. At no part in the growing - transport - shelving - selling chain can anyone be expected to thoroughly wash between the leaves, especially near the root. Rinse your veggies before using.
I don't know where you live but I'm in Australia and I also lived in South America and I've seen plenty of dirt, caterpillars, aphids and flies too many times on my lettuce, harvested from different sources, seasons, and purchased from different supermarket chains and small grocer shops.
And it was never a problem for me. Where are you getting your sterile lettuce from, so I make sure I don't?
The correct answer is 9/12 pesticides are removed by Simple rinsing with water. Detergents do not improve results compared to mechanical removal via rinsing for 30 seconds.