so flight from YYZ to CDG left late last night (Saturday night) and arrived late in the morning (as you would expect for a late departure)

My question then, why are we told the return flight is on time until ten minutes before boarding and then told it will be delayed an hour due to the lateness of the inbound aircraft?

anyone else find this happens a little too frequently?
(surely they should have known and posted that the flight would be delayed long before ten minutes before boarding)