This confuses me.Manifestos mean SFA anyway. Lots of promises which are never kept. I recall the last GE Labour manifesto gave a commitment to "respect the result of the Brexit referendum". They didn't. They argued and bickered and then came up with no policy whatsoever.
Manifestos are just pages of empty, hollow "promises". That is the way they have always been.
A manifesto is a commitment to what a party will do in Government. If the party loses a general election the manifesto is ripped up and not acted on - for the simple reason that the party isn't in Government, and in any case the manifesto was rejected by the electorate. So who sticks to a manifesto after losing an election....?