We can only speculate of course, but

a) they never actually had it working, it was a mockup
b) they switched priorities and think every pair of hands is needed for work on Android
c) the Nokia team he refers to is not Adobe's team but ACTUAL Nokia
d) the Nokia team switched priorities to Symbian
e) he doesn't say it's coming to the N900. He ambiguously says something along the lines 'it ships with 9.4, we'll show a prerelease of 10.1 and will release it to Nokia devices in 2010'
f) TI never delivered on the hardware acceleration/driver front
g) Nokia is dropping/freezing Flash support altogether and moving to the WebKit/HTML5 camp
h) It's not ready yet and will not be ready in the timeframe the N900 will get updates
i) _______ (favourite conspiracy theory)


You can pick multiple choices if you want to.