I used to be a one bag person too. Way back when, when I first started buying Coach, I would buy one and carry it about a year, then give it to Goodwill and buy another. In those days, I usually bought brown Coach bags because the leather was so pretty. Then I got married and we lived overseas for awhile. I can't remember what bags I carried then. I know that once I had kids, I pretty much focused all my spending on them, and started carrying no name leather bags, like the kind they sell at Penney's. I only cared about the utility of the bag, that it had enough pockets to keep me organized. I wouldn't replace it until it started looking shabby.
Now I figure that instead of carrying one bag until it falls apart, I carry each bag for short periods of time, but own them for many years. I guess you could say that if I have 25 bags, I have 25 years worth of bags. Eventually they might get as much use as if I carried them serially until they wore out, but I'm having more fun doing it this way.
The practice of getting different bags for different things, like a tote for work, an evening bag, a crossbody for travel, and satchel, etc. doesn't apply to me, because I don't really have a lot of different types of occasions. I don't work at an office and we don't go to fancy events. I carry whatever bag I happen to be using to everything. The only time I choose a particular bag for an occasion is when we travel; then I make sure I pick a bag that wears well in any kind of weather, goes with most of my clothes, and is large enough to hold everything I could possibly want.