Why is "sherbet" pronounced "sherbert" so much?
Solution 1:
I looked at spelling in print over the last century. This NGram chart gives the an exaggerated impression of the difference. Usage figures are 160,000 for sherbet, and 28,500 for sherbert.
That's more than 1 in 6 actually writing the r, almost certainly in contravention of what they'd find if they'd looked it up in whatever dictionary they had to hand. One could reasonably assume at least that fraction would say it that way, if not many more.
OP implies the less common form is simply 'wrong', but I see no reason to think this. It's just an alternative spelling associated with alternative pronunciation. So far as I can see, that alternative spelling has been around for several hundred years, so I guess the pronunciation has too.
Solution 2:
Two reasons:
- They first heard it that way. This is actually the more popular pronunciation in the US, even though it is incorrect.
- Sher-bet is harder to say because it requires a longer pause between the first and second syllable to bite off the "bet".
Solution 3:
Another very similar example is the pronunciation perservere for the standard persevere.
This is a famous example of
epenthesis
with a smattering of
assimilation
The phenomena (not yet an explanation of why) is the addition of a sound (the epenthesis ), and the sound added is by assimilation (specifically progressive assimilation meaning the first sound affects the second).
As to why, well, it doesn't always happen, and in fact the opposite often happens (dissimilation, e.g. apeture for aperture, govenor for governor (note that this is for pronunciation not spelling)). So predicting when it will happen is not so clear. But we know, by the existence of other examples, that the phenomenon is not isolated.