I'm a grown man with a fat bank account and I drink water from the tap as do my four kegged friends. I am lucky enough to be able to choose to live in a developed city with clean drinking water. Which really should be the norm. I know this story is supposed to be uplifting but it makes me sad.
These people could also be living on a well which typically have hard water. Most of them are safe to drink from but it won't taste great so it would make sense to filter it. There's nothing that hints at where they live so I wouldn't get to bothered by it.
Just because the water coming out of the main treatment plant is good, doesn't mean it's free of contaminants by the time it reaches your tap. Why not filter it once more before, you know, incorporating it into 70%+ of your body mass?
Because those filters don't filter out the stuff you'd actually wanna filter (lead) and they can grow mould and make your water worse instead. (I got this from a consumer testing org like wirecutter)
The top contaminants filtered by fridge filters are chlorine, lead, mercury, pesticides, and pharmaceuticals. And, yes, like any other filter, you need to change them regularly.
What they filter and how effectively they filter it is entirely predicated on what type of filter you use and if you regularly replace it, just like and other water filter.
We moved to a new city and for the first time we had to buy a water container with a filter. I've never tasted tap water with so much chlorine in it and I was always the first one to say it's stupid not to drink directly from your tap.
So yeah, you don't know the people's situation in OP's screenshot, maybe the tap water just tastes bad.
Loads of people in cities with perfectly clean and healthy tap water still use water purifiers because they like supporting the filtration industry, or worse believe in crystals doing magic to their water.
I've lived my entire life in the two best tasting water serving cities in America, and I grew up with and decades later continue to use, water filtration. I don't understand the flex you're doing here. And what is sad? Also, you do know much of the industrialized world outside the States drinks bottled water, right?