Well, I don't know about all the bowl changes. I admit that I'm probably not the most responsible fishy owner but I have a hard time killing them. My betta lives in a fairly large vase with a live plant. I clean it about once a month (adding water inbetween because of evaporation). Once I noticed a lot of old floating food/slime on top so I cleaned it and started feeding him less and I haven't had the problem since. When I do clean the vase I put him in a measuring cup with the original vase water, do a quick clean of his bowl (no hard scrubbing of the rocks or plant) and then add him and the water back into the vase that is filled with tap water - no conditioners. It's always worked for me this way and my fish have always been quite healthy and live for years.
My daughter also keeps two comet goldfish in her room (I look after them). Her first one just died - but we had him for two years and he looked completely healthy when I found him. I quarantined his bowl mate (had him for 1 year) for 2 weeks and when nothing happened I added another younger comet last week and they are both doing great. I do the same routine with their bowl although they don't have a live plant because they ate the last one.
I know I'll probably get blasted for this, but I honestly think that fish like bettas and goldfish die so easily because their owners are always fussing over their bowls/tanks. It's just strange that I do so little and my fish live for so long.....