It doesn't fall any more than with a spoon, unless we are talking about something extremely crumbly such as thousand layer cake. Which to be fair is also a pain to eat with a spoon, or any kind of cutlery. I find the flat profile of the fork is excellent to cut a small portion of the cake away without upsetting the rest of the cake structure. I can't say the same about the curve of the spoon, which forces a scooping motion that often messes up the cake. I also find that the curved edge of the spoon makes it difficult to lift any crumbs from a flat plate surface. If I can't lift crumbs with the fork's edge, I can always press them down flat between the prongs and lift them. The curved shape of the spoon doesn't allow for this. Finally, I prefer how the fork feels in my mouth as opposed to the spoon.

So, these are my reasons for preferring a fork over a spoon when eating cake. Interesting to see people making a case for the opposite, but hey that's exactly what I wanted to know.

Edit: clarification on first sentence

I'll show this to the staff in the places I frequent next time they give me a spoon with my cake order, thanks