I am wondering if the loss in popularity of the dipthong ("squished-together vowels" - a delightfully apt description!
) is, at least in part, due to the relative difficulty in producing them on word processing software. They are fairly rare in English, anyway, so the temptation to reduce them to a single vowel is quite intense.
If this is so, it is rather a pity, as yet another example of how our culture is increasingly being defined by our technology.
A probable second reason - and one which was apparent before the advent of mass-PC/Mac ownership - is uncertainty among many people of how to pronounce words with dipthongs.
