https://pubmed.ncbi.nlm.nih.gov/29991030/
In adults, fat cell number is constant over time in spite of a large turnover (about 10% of the fat cells per year) when body weight is stable. A decrease in body weight only changes fat cell size (becoming smaller), whereas an increase in body weight causes elevation of both fat cell size and number in adults.
https://pmc.ncbi.nlm.nih.gov/articles/PMC4371661/
This one's not as easy for me to quote.
Basically the gist of the whole idea is that your body maintains the level of fat cells pretty steadily as an adult. When you gain or lose weight the cells just grow or shrink, but they can only grow so big before you need new cells to store more energy and your body will build them. Each of the fat cells have a part to play in signaling that you're in a deficit and need to consume more calories (when we didn't have such calorie dense foods readily available this was probably correct most of the time). So, if you have 2 or 3 times the number of fat cells then you "should" that's increasing the signaling you receive to eat, making it harder not to (simplifying that a lot). In normal maintenance, your body still maintains that turnover pretty steadily so it generally doesn't go away.