1. Sensory reasons. Personally there are some types of reusable straw I can use, but others are utter sensory hell. Drinking without a straw hurts my teeth. None of them are as good sensory-wise for me as a disposable plastic straw. If I’m already overloaded I’m going to grab the disposable straw. It would be the difference between a meltdown and not for me. I would be very surprised if there is not a good population of people with sensory issues who absolutely cannot use any reusable straw on the market.
2. Spoons/energy reasons. I just spent 15 minutes washing my 8 reusable straws (I have a bunch because it’s easier for me to do them in batches). I am now ready to lie down for a few minutes. I absolutely do not blame anyone who can’t spare the spoons to wash straws. I do not blame anyone who theoretically could but would rather use their limited time and energy on something else.
3. Basically any reason, even if you can’t articulate it. People need to mind their own damn business. Anything individuals do is a drop in the bucket anyway. Maybe the person chooses to use a straw if it improves their life in some small way but makes effort to help the environment in other, less trendy or visible ways. Please use your awesome energy and motivation for helping the environment to protest the large corporations who are actually causing the bulk of the problem and leave disabled and other marginalized people alone.