This has been SOP on all airlines for me for years. It's alleviated a bit when you live or are flying from a hub city on the hub airline, because reroutings are easier.
I had a flight booked on AA in May from SFO-ORD-MSP. Because of aircraft taken out of service for hail damage at DFW, my SFO-ORD leg got cancelled. AA could not get me to MSP for 3 days. I said screw it and ended up buying an F ticket on DL to get there (UA also had availability-but was much more expensive).
So i think that although its a difficulty because of the load factors, I at least find comfort that the airlines are able to fill their planes, make money, and maybe have more frequencies in the future if the route is profitable