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Full flights don't always mean profitable flights. If a flight isn't filling up, the airline will open up the inventory for lower fares. So flying a full 737 with mostly $200 cheapie fares doesn't necessarily make good business sense.

Cleveland is also a tricky one for CO, as there isn't as much origin/destination traffic there as the IAH or EWR hubs. So, with such a high volume of passengers connecting, that further worsens the economics of such a flight.

So, if CO thinks they can better utilize the aircraft elsewhere, that's proabably what they're doing. It's unfortunately it's a favorite flight of yours. If revenue comes back, maybe the flight will as well.