Here's what i feel happened:
The showrunners (obviously) always had
this ending in mind. (duh, they shot it, scene with the kids and all).
The show got immensely successful and got renewed over and over again, 2-3 seasons too many for its own good.
Throughout the last 3 seasons, all the build-up about when we'd
finally meet the mother was too much, that whole will-they-won't-they Robin shit was re-used too many times, always with increasing degrees of finality. (*cough* the beach scene ...)
(Too many times, Barney met that one soulmate that made him let go off his 'Barney' ways. Too many times Ted realized that Robin and him would never work out - this time
for realsies.)
So the whole cocktail of: A shitty last season, over-stretching the audience's patience too many times, as well as their biggest mistake - making the mother just
too perfect and loveable for the show's own good, as well as how we then were
rushed from meeting her to having to let go off her within a few episodes - is what frustrated so many people.
Imho they should've course corrected. Read the room. Discard the pre-shot footage (they just were too much in love with their clever 'the ending was known almost 10 years ago' idea), and maybe make that the DVD-release extra ending.
I feel like the last season is what will make HIMYM - in my mind - a failed attempt to replicate Friends, which was on a great trajectory but due to a very "risky" premise had to one-up itself again and again and would finally - by not sticking the landing - go down in TV history as the inferior product.
Code:
[IMG]https://i.imgur.com/xl2k37d.png[/IMG]
Code:
[IMG]https://i.imgur.com/uprm04w.png[/IMG]