I love betta fish and I have to say with all the pain in my heart that before I became a good fish keeper, a lot of bettas died in my "care" (some of the worst are a veiltail that I had in a bare-bones 2 liters cylinder that died after a week and a royal blue double point crowntail that I named Poseidon that died after a few days poisoned by the not aquarium-safe gravel I used in its 1-liter bowl), and this was because of the lies I was told about their care that I believed without even looking further into it.
The whole mud puddle thing makes me so angry since yeah it is a 50-100 cm deep body of stagnant water but it is like 5 square meters area like common, and even at that a lot of bettas come from rivers and straight-up lakes and wetlands, not some random rain puddle.
the problem is that people see them as living decor and not as animals, as such, they put as much care into their bettas as they do for a silk flower arrangement. My family is guilty of this behavior but I am trying to change that slowly, my mom and dad are already out of the fish abusing loop since I live with them and can keep tabs on all the fish-related issues of the house, in my mother's side of the family there is also no fish abusing problems since they currently don't keep fish and the members that wan to do so in the near future already decided that they are gonna let me help and listen to what I tell them. The real problem here is my dad's side of the family mainly my dads younger sister, first some backstory:
My dad is the oldest of 7 siblings and my problem aunt is the youngest daughter as such she was always the spoiled one and still is, she is kinda entitled, and if she does something it's guaranteed that at least one of my aunts and uncles will copy her. Now for the fish abuse (yay!).
She for a lot of time now has kept multiple bettas in the same ugly ass 10-liters flower vase that she only fills up to the middle, this flower vase has an area of like 10 square centimeters and the rest of the volume is from vertical space, she has clown puke gravel and no filter, heater or plants. she does these ugly water changes where she just dumps everything out and washes it with tap water (which here in Mexico has a mega load of chlorine). And whenever the fish dies she just buys another one, and as such she believes that bettas don't live more than a year, not that long ago she along with some other family members from my dad's side discovered that I breed fish and aquatic invertebrates and I used this chance to try and make her new betta's life as good as possible so while she asked me about the whole fish breeding thing I and murky water told her that the flower vase was no place for a betta and started selling the whole nano aquascape thing to her telling her it would be a better house for a betta and it would be a far better decoration piece than a flower vase with gravel, it all was great until I told her the best size would be a 20-litters (5 gallons) aquarium, then she said "you are crazy, that's way too much water, it is a full water jug", I then explained what a partial water change was and she seemed a bit more into the idea but not fully, i currently am still trying to get her 100% on board with a 5 gallon nano planted aquascape for her betta, and if i am lucky then the rest of the family will do as they usually do and copy her example (if we are mega lucky they will also ask for my help).
I keep my 2 bettas in 15 liters (4 gallons) Tupperware but I do so because I don't have enough space to keep them anywhere else right now but I am in the process of buying and installing a rack system in my room, then I will buy some nice 5 gallon tanks and have them there with some more species only aquariums for the rest of my fish and invertebrates, their current house is wider and longer than it is taller which is something bettas like and I have it with sand, rocks, leaf litter and plants, they are doing fine and my male is happy enough that he made a bubble nest while my female became gravid, I keep up with my water changes and I feed live foods regularly so I think I am not doing that bad for someone with bettas on Tupperware, also their current homes are better than the 1-liter bottles with nothing in them whatsoever in which they were at before.