.......they already have your money so putting you in that empty seat is no financial advantage...
but .... they then have a better opportunity to sell my later seat to someone else, which would be a financial adv. maybe, nothing lost in getting rid of me earlier.
The excuse given was the "manpower" involved in changing the ticket. Bollocks, if I had requested an earlier flight before departing from my original destination than I would agree, but if my previous flight arrives early, and I have the chance to make an earlier connection, why not, I had no baggage, held a boarding card issued by the previous station - yes, the "wrong" flight number might have had to be re-issued - and was at the communal departure/arrival hall, just enter by one door and depart from the adjacent one. Easy ? No !